In this review, we examine the continually expanding and increasingly compelling data linking radiation and various chemicals in our environment to the current high incidence of breast cancer.Singly and in combination, these toxicants may have contributed significantly to the increasing rates of breast cancer observed over the past several decades. Exposures early in development from gestation through adolescence and early adulthood are particularly of concern as they re-shape the program of genetic, epigenetic and physiological processes in the developing mammary system, leading to an increased risk for developing breast cancer. In the 8 years since we last published a comprehensive review of the relevant literature, hundreds of new papers have appeared supporting this link, and in this update, the evidence on this topic is more extensive and of better quality than that previously available.Increasing evidence from epidemiological studies, as well as a better understanding of mechanisms linking toxicants with development of breast cancer, all reinforce the conclusion that exposures to these substances – many of which are found in common, everyday products and byproducts – may lead to increased risk of developing breast cancer. Moving forward, attention to methodological limitations, especially in relevant epidemiological and animal models, will need to be addressed to allow clearer and more direct connections to be evaluated. In this review, we examine the continually expanding and increasingly compelling data linking radiation and various chemicals in our environment to the current high incidence of breast cancer. We acknowledge the importance of many widely understood risk factors for breast cancer including: primary genetic mutations, reproductive history, and lifestyle factors such as weight gain, alcohol consumption and lack of physical exercise , 2. Yet This report focuses on these environmental issues. In the 8 years since we last published a comprehensive review of the relevant literature , hundredThe goal of this review is to offer a broad overview of the scientific literature examining the potential connections between exposure to environmental toxicants and changes in the risk for developing breast cancer, updating our last review of this topic published in 2009. To fully incorporate the relevant materials, we entered the following search terms into both PubMed and Scopus: ‘breast cancer’ and ‘mammary tumors’ in conjunction with ‘environment’, ‘endocrine disruptors/endocrine disrupting compounds’ and all of the individual toxicants covered in this report.In selecting epidemiological studies, we emphasized work from the past 10 years. When studies were follow-up reports from large, longitudinal studies, we also reported the earlier data as the length of time between exposures and outcome assessments could lead to different conclusions, or recognition of different results as the participants in the study reached later ages and, especially, progressed from pre-menopausal to post-menopausal status.Over the 8 years since our last report, there has been a substantial increase in the amount of information focused on mechanisms underlying the complex relationships between exposures and risk for developing breast cancer. This is especially true in the growing field examining exposures to endocrine disrupting compounds and disease risk. We therefore focused on articles from the past 8 years. While we did not report every gene whose expression might be affected by a particular exposure, we did try to give a full overview of the current understanding of physiological, developmental, genetic, epigenetic and endocrine processes that are affected by exposures relevant to a change in risk for developing breast cancer. Although the emphasis was on the most recent data, we included earlier results when they were needed as background or to provide a fuller picture of the evidence.Exceptions to our primary reliance on very recent literature are found in the sections on non-endocrine disrupting industrial chemicals and some pesticides and herbicides. Much of the relevant data for these toxicants comes from studies from 25 to 30 years ago, when the National Toxicology Program (NTP) and International Agency for Research on Cancer (IARC) were determining possible carcinogenicity of these chemicals.Finally, in selecting studies to report, we took care to include studies that had negative results, that is, those that reported no significant relationship between exposures and risk for developing breast cancer. Where possible, we then explored possible differences in study design or methods that might account for differences in results across studies.We report the statistics , along with 95% confidence levels, as offered by the authors of the individual reports. Where explicit adjustments were made, we note the type of statistic used and the variable of adjustment. More often though, factors including age, menopausal status, breast cancer subtype , racial/ethnic identity, are reported as main factors to be analyzed, along with effects of particular exposures. Significant main effects and interactions between exposures and these other variables are reported in this review.In this introductory section, we provide basic statistics and a brief exploration of the several subtypes of breast cancer – recognizing that the term ‘breast cancer’ is often used as a proxy for several distinct genetic, histopathological, and hormonal profiles for the disease. We then introduce a series of key framing concepts necessary for appreciating the complex evidence supporting (or not) a growing understanding of the data implicating specific environmental toxicants in an increased risk for developing breast cancer. These framing concepts include: (a) low-dose and non-monotonic responses; (b) interactions between environmental toxicants; (c) gene-environment interactions and epigenetic changes; (d) cell-cell interactions and the Tissue Organization Field Theory; and (e) timing of exposures. We conclude with a schematic model of the complexity of factors influencing risk for developing breast cancer, with an emphasis on environmental factors.The Surveillance, Epidemiology, and End Results (SEER) program of the National Cancer Institute (NCI) predicted that in 2015 in the U.S., 40,290 women and 440 men would die of breast cancer and 231,840 women and 2350 men would be diagnosed with invasive breast cancer; another 60,290 women would be diagnosed with breast cancer in situ. As of early 2016, the NCI estimated that approximately 3,560,570 U.S. women are living with a prior diagnosis of breast cancer .The most recent year for which accurate data exist related to breast cancer incidence and mortality is 2012. In addition to total national incidence and mortality reports, SEER data are broken down by major census self-described categories of race/ethnicity. The average incidence rates  across the 5 years from 2008 to 2012 differed across census categories, as did the trends across time. Five-year average incidence rates for whites were the highest (126.1), with rates for black women only slightly lower (124.1). However, in 2012 for the first time since SEER began collecting data in 1975, incidence for these two groups converged; historically black women had a significantly lower rate of the disease. Average 5-year incidence rates were lower for American Indian/Native American (91.9), Hispanic (91.9) and Asian-Pacific Island (88.3) women pyrene) as a proxy for all traffic related PAHs, researchers compared breast cancer incidence in women exposed to the top 5% of traffic exposure to those with below median exposure levels. Higher exposures to traffic-generated PAHs were associated with an increased incidence of breast cancer in women who ate low levels of fruits and vegetables . A significant association was not found for women who ate high levels of these foods. The association with higher incidence of breast cancer was found only for ER−/PR− tumors .In a case-control study, burning synthetic logs, but not wood-only logs, in woodstoves or fireplaces was also associated with an increased risk of breast cancer . The association was stronger in women whose exposure was after age 20 and for at least 7 years duration of use. Women who burned synthetic logs and developed breast cancer were more likely to have at least two genetic variants in genes that regulate glutathione-S-transferases, enzymes which are important as cell detoxifiers  .One of the studies from the Long Island Breast Cancer Study Project found that women with the highest level of PAH-DNA adducts had a 50% increased risk of breast cancer . More spIn an earlier report, researchers explored the presence of PAH-DNA adducts in breast samples taken from women diagnosed with cancer as compared with those diagnosed with benign breast disease. Cancerous samples were twice as likely to have PAH-DNA adducts as were benign samples . Follow-BRCA1 or BRCA2 mutation. In a small case-only study of 23 men with breast cancer, four of whom were carriers of a BRCA1/2 mutation, BRCA1/2 carrier status interacted with history of ever having driven trucks professionally to enhance the risk of developing breast cancer  [Occupational exposure studies have looked at workers exposed regularly to gasoline fumes and vehicular exhaust, major sources of PAHs (as well as of benzene). These occupational exposures are associated with an increased risk of breast cancer for pre-menopausal women   and also.1–1415) .A case-control study in western New York indicated that very early life exposure (around the time of birth) to high levels of total suspended particulates, a proxy measure for PAH levels, is associated with increased risk of breast cancer in post-menopausal women . An exteThe studies above all looked at breast cancer incidence. Two reports examined the relationship between PAH exposures and mortality. Using an ecological model exploring the association between suspended fine particulate matters in several municipalities in Taiwan, researchers found that women living in areas with high levels of particulate matter in the air had an increased probability of dying from breast cancer, as compared to those living in cleaner areas  . AnotherA 2007 report from the Long Island Breast Cancer Study Project demonstrated that self-reported lifetime use of residential pesticides was associated with an increase in risk for breast cancer. The increase was found for women who had reported use of pesticides in the aggregate , as well as specifically for use of lawn  and garden  pesticides, although there were no relationships between perceived doses of exposures and risk for cancer . These rTriazine herbicides  are the most heavily used agricultural chemicals in the United States. Atrazine and simazine have been banned in the European Union, and cyanazine is labeled as a highly toxic mutagen, because of their high presence in drinking water, demonstrated harmful effects on wildlife, and potential health effects in humans. Cyanazine was phased out of use in the U.S beginning in 1996, although simazine and atrazine are still approved for use in the United States. More than 75 million pounds of atrazine, the most heavily used of the chemicals, were applied annually in the United States in 2008  has data), primarily to control broadleaf weeds in corn and sorghum crops in the Midwest .Elevated levels of atrazine are found each spring and summer in both drinking water and groundwater in agricultural areas –411. AtrHigh levels of triazines, mainly atrazine, in contaminated waters were associated with an increased risk  of breast cancer  althoughA weight-of-the evidence review of seven epidemiological studies, funded by Syngenta — the producer of atrazine, concluded that across study designs, there was no causal relationship between exposures to atrazine and development of breast cancer. However, availability of only relatively few studies, lack of attention to breast cancer subtypes and other methodological complications makes ruling out an association unsupportable .Research in rodents has shown that atrazine exposure disrupts pituitary-ovarian function, resulting in decreases in circulating prolactin and luteinizing hormone levels, changes that contribute to the effects of this herbicide on increases in mammary tumors , 421. AtExposure to atrazine or mixtures of atrazine metabolites during gestation delays development of the rat mammary gland in puberty, widening the window of sensitivity to breast carcinogens –426. SimAlthough atrazine is an endocrine disruptor in estrogen-directed pathways, several studies have indicated that atrazine does not exert its effects through binding to ER , 430. OtP = .078) between heptachlor concentrations and breast cancer risk was found.Heptachlor is an insecticide that was widely used in the United States throughout the 1980s, especially for termite control. In 1988, the U.S. EPA restricted use of heptachlor to certain applications for controlling fire ants, but agricultural use continued until 1993 because growers were allowed to use up existing stocks . HeptachHeptachlor still contaminates both soil and humans. Its breakdown product, heptachlor epoxide (HE), is known to accumulate in fat, including breast tissue. Levels are highest in women ages 20 and older, but HE is also found in the bodies of adolescents 12 to 19 years old  and in eAlthough HE does not act like estrogen, it affects the way the liver processes hormones, thereby allowing levels of circulating estrogens to rise and increasing breast cancer risk. HE also has been shown to disrupt cell-to-cell communication in human breast cells in culture  and to iFrom the 1950s until 1970, the pesticides dieldrin and aldrin  were widely used for crops including corn and cotton. Because of concerns about damage to the environment and, potentially, to human health, in 1975 the EPA banned all uses of aldrin and dieldrin except in termite control; the EPA banned these pesticides altogether in 1987 . Thus, mtrend = <.01) [Hoyer et al. showed a clear relationship between breast cancer incidence and dieldrin in their examination of a rare bank of blood samples taken from women before the development of breast cancer . During  = <.01) .Treatment of mice prenatally and neonatally to environmentally relevant doses of dieldrin increased the number and size of mammary tumors. These effects may have been mediated through changes in the cellular expression of the growth factor BDNF and cell-signal receptor Trks. Both of these were elevated in tumors from the dieldrin-treated animals .Like many other pesticides found in the environment, dieldrin has been shown to be an endocrine disruptor, both by stimulating estrogen-regulated systems and by interfering with androgen-regulated pathways. Addition of dieldrin to human breast cancer (MCF-7) cells in vitro can stimulate their growth and proliferation .A case-control study of 128 Latina agricultural workers newly diagnosed with breast cancer in California and 640 cancer-free controls, identified three pesticides—chlordane, malathion and 2,4-D—associated with an increased risk of the disease. Scientists found that the risks associated with use of these chemicals were higher in young women and in those with early-onset breast cancer than in unexposed women .Engel et al. studied the association between pesticide use and breast cancer risk in farmers’ wives in the NCI’s Agricultural Health Study. This large prospective cohort study enrolled more than 30,000 women in Iowa and North Carolina. Researchers found evidence of increased incidence of breast cancer in women using 2,4,5-trichlorophenoxypropionic acid  ; a non-significant association was found for dieldrin and captan. Incidence was also modestly elevated in women whose homes were closest to areas of pesticide application  .Young children of farmers using 2,4,5-TP on their farms had high levels of the pesticide in their urine samples soon after the chemical had been applied to the fields . This isTreatment of female rats with malathion resulted in abnormal increases in mammary duct proliferation and induction of mammary tumors when animals were tested at 8 months of age .Dichloro-diphenyl-trichloroethane (DDT) was the first widely used synthetic pesticide. It is credited on the one hand with the eradication of malaria in the United States and Europe and on the other with long-term devastating effects on reproductive success in wildlife and adverse health effects in humans . Banned p = .02). On the other hand, a study from the Long Island Breast Cancer Study Project did not find an association between DDT/DDE  and breast cancer [Epidemiological data are mixed regarding the effects of DDT/DDE on breast cancer risk . A case-t cancer . Both oft cancer .Two critical studies that examined early life  exposures to DDT have demonstrated a clear association between exposures to DDT and increased risk for developing breast cancer , 104. A In a case-control prospective study of 9300 women in the CHDS pregnancy cohort (daughters of the mothers in the larger CHDS cohort), stored postpartum maternal blood samples were analyzed for levels of DDT. Daughters were followed for 52 years and breast cancer diagnosis in this cohort was determined. DDT levels in perinatal blood of mothers from breast cancer cases were compared with levels in perinatal blood samples from mothers of age-matched controls. Higher maternal DDT levels were associated with a significant increase in occurrence of breast cancer in their daughters by age 52  .A comparison of the association between disease risk and DDT use in developed countries  and in developing countries  supports the premise that exposures to DDT are associated with increased risk of breast cancer. The association between DDT levels and breast cancer was much stronger in developing countries, where women of the age to be diagnosed with breast cancer also would have been exposed to DDT during critical periods of development .A study from the Long Island Breast Cancer Study Project examined post-diagnosis mortality and serum DDT levels at time of diagnosis. Higher levels of DDT 5 years after diagnosis were associated with an increased mortality rate  although the effect was not significant at 15 years post diagnosis .Laboratory studies have found that in addition to being directly genotoxic or carcinogenic , the estAlthough the EPA banned the use of PCBs in new products in 1976, substantial amounts of the insulation fluids, plastics, adhesives, paper, inks, paints, dyes and other products containing PCBs manufactured before the ban remained in use for decades . About oLevels of PCBs were high before being banned in the United States, but generally their presence in the environment and in human tissues has decreased slowly over the past decades , 471. ChThe more than 200 individual PCBs are classified in three types based on their cellular effects. Group I PCBs are estrogenic; Group II compounds are anti-estrogenic; and Group III PCBs appear not to be hormonally active, but can stimulate the enzyme systems of animals, including humans, in a manner similar to certain drugs  and other toxic chemicals , 474. AdThere are several epidemiological studies that have implicated exposures to PCBs as a risk factor for later development of breast cancer. Women who regularly ate PCB-contaminated pike or perch had higher risk for breast cancer than women who never ate these fish  . AnotherMost studies have looked at total PCB levels without identifying individual types. A few studies, however, have looked at relationships between cancer status and particular PCBs or groups of PCBs. For example, a recent meta-analysis demonstrated that there was no relationship between exposures to Group I PCBs, but there was a significantly increased risk of breast cancer with exposures to either Group II  or Group III  PCBs . Anotherp for trend <0.01) [In a case-control study, Aronson et al. measured several types of PCBs, along with DDE, in tissue samples from women scheduled for excision biopsy of the breast. Increased risk for breast cancer was associated with higher concentrations of Group II PCBs 105 and 118, with the ORs for these two PCBs increasing linearly with higher concentrations (d <0.01) .On the other hand, some studies have found no link between PCBs and breast cancer . A 2009 exon 7) of the CYP1A1 gene was associated with an increased risk for breast cancer  [Some of these compounds may have their greatest impact on women with particular susceptibilities and looking broadly at large samples will not tell the full story of cancer risk as influenced by PCB exposures. For example, researchers evaluating data from the Nurses’ Health Study revisited the issue of PCBs and breast cancer risk and revised their conclusion concerning the link between PCBs, DDE and breast cancer. In studies of PCBs and DDE in blood, they had previously concluded that exposure to these chemicals was unlikely to explain high breast cancer rates . Newer eenotype) .As was true for the critiques of the DDT studies cited above, the methods used to test these relationships do not account for exposures to PCBs during earlier developmental times when mammary tissue is particularly sensitive to the toxic effects of many environmental chemicals . The resDioxins are formed by the incineration of products containing PVC, PCBs and other chlorinated compounds as well as from industrial processes that use chlorine and from the combustion of diesel and gasoline . One of Dioxins accumulate in the body fat of wildlife and humans, and they break down very slowly, with a half-life of 7–11 years in body tissues . People CYP1A1 and CPY1B1 genes [There is a substantial decrease in the amount of dioxin remaining in a women’s breast fat tissue after she has breastfed because the chemicals have been passed on to her newborn via breast milk . AlthougB1 genes .A study of women exposed to dioxins during a chemical plant explosion in 1976 in Seveso, Italy demonstrated a time-dependent association between dioxin exposure and breast cancer , 497. A A retrospective mortality study in Germany examined deaths from cancer among people who had worked in a chemical factory in which they were exposed to high levels of TCDD. As compared with national mortality rates in West Germany, 5 years after closure of the plant, there was no increase in overall mortality from cancer for female workers, although there was a significant increase in deaths from breast cancer among those who worked in high-exposure regions of the factory (SMR = 2.15) . A laterSeveral laboratory studies have demonstrated that the timing of exposures to dioxins matters. Although exposing animals to dioxins in adulthood may not affect cancer rates, earlier exposures may have profound effects. Administration of dioxins  to pregnant rats leads to structural abnormalities in the development of their pups’ mammary tissues and higher incidence of tumors when the pups grow to adulthood –504. TCDTCDD has been shown to inhibit estradiol-induced cell growth and proliferation as well as other pathways regulated by estrogens, including methylation of CYP1A1, in a variety of human breast cancer cell culture lines , 507. LiBRCA-1 expression, a result of increased BRCA-1 promoter hypermethylation [Prenatal treatment of rats with low doses of TCDD led to increases in the number of terminal end buds (TEBs) counted in whole mount preparations of postnatal day 71 females. The treatment also resulted in a suppression of hylation .PBDEs are a complex group of chemicals that are structurally similar to the polychlorinated biphenyls (PCBs). Products containing PBDEs include polyurethane foam in furniture (penta-BDE) and electronic and plastic products (octa- and deca-BDEs) .Although both penta- and octa-BDEs have been banned in the European Union and have not been produced in the United States since 2004, products containing them remain throughout the world. PBDEs are found ubiquitously in the environment and are detected in air, dust, soil and food as well as in many wildlife species. Although home exposures (as measured by dust levels) have decreased over the past decade, levels remain high enough to remain a serious health concern .There is considerable geographic variability in exposures to the chemicals; people in California, with its historically stringent furniture flammability standards, have much higher levels of PBDE exposures than do people in Massachusetts. Within the California group, lower socioeconomic status was associated with higher PBDE levels , 517. MeData from young girls (ages 6 to 9) from California and Ohio support these findings. Although PBDEs were found in almost all samples tested, girls in California had significantly higher blood serum PBDE levels than did girls from Ohio, and young black African American girls had higher levels than either white or Hispanic girls . In thes4) in regulating brain development [PBDEs have been found in human fat tissue, as well as in blood serum, breast tissue and milk –523. PBDelopment , 526.Very few data directly address the possible effects of PBDEs on breast cancer risk. One case-control study found no relationship between PBDE levels in breast fat and breast cancer risk, but the sample was small and the chemical analysis was done around the time of diagnosis of breast cancer in the women who developed the disease . HoweverEven as PBDEs are being used less often as fire retardants in common consumer products, there is now evidence that the chemicals being used as substitutes — including Firemaster 550®, a common substitute with proprietary ingredients — are increasingly contaminating our environment , 534. AlAromatic amines are a class of chemicals found in the plastic and chemical industries as byproducts of the manufacturing of compounds such as polyurethane foams, dyes, pesticides, pharmaceuticals and semiconductors . They arThree monocyclic amines, including o-toluidine, have been identified in the breast milk of healthy lactating women , as wellOccupational exposures of female rubber-factory workers to another set of monocyclic aromatic amines derived from p-phenylenediamine are associated with an increased risk of breast cancer in the following several years. The amount of increased risk was correlated with total cumulative exposure levels to the aromatic amines, with lowest levels leading to a 3.7-fold increase in cancer and the highest levels of exposure increasing risk more than tenfold .A case control study of women who used hair dyes, in comparison with those who have not, revealed an increased risk of breast cancer in the dye users . In addition to intentional inclusion of p-phenylenediamine , major cHeterocyclic aromatic amines (HAAs) are formed  when meats or fish are grilled or otherwise cooked at high temperatures. In a case control study, Steck et al. found an association between higher lifetime consumption of grilled meats and fish and increased incidence of post-menopausal breast cancer  . StudiesAromatic amines are metabolized by N-acetyltransferases. This metabolic process ultimately leads to other compounds that are thought to be the actual carcinogenic chemicals. There is an extensive literature examining whether or not genetic profiles that alter the efficacy or speed of N-acetyltransferase activation, especially through the N-acetyltransferase 2 (NAT2)-regulated pathway, might alter susceptibility to breast cancer. Studies have reached differing conclusions about the role of possible polymorphisms of the NAT2 gene on breast cancer susceptibility. A 2010 study tried to disentangle many of the possible confounding factors and found that eating grilled meat (and drinking coffee) resulted in greater risk for diagnosis of ER- breast tumors in women with the ‘slow-acetylator’ form of the NAT2 gene .Laboratory studies of HAAs in systems using cultured breast cancer cells demonstrated that these chemicals can mimic estrogen, and they also can have direct effects on cell division processes in ways that might enhance the development of tumors .Higher accumulations of iron, nickel, chromium, zinc, cadmium, mercury and lead have been found in cancerous breast biopsies as opposed to biopsies taken from the breasts of women without breast cancer. These metals also have been found in higher concentrations in serum and urine from women diagnosed with cancer as compared with those from healthy women –552.Laboratory studies have shown that a number of metals including copper, cobalt, nickel, lead, mercury, methylmercury, tin, cadmium and chromium have estrogenic effects on breast cancer cells (MCF-7) cultured in vitro –555, witSeveral epidemiological studies have demonstrated an association between higher cadmium levels in urine  , 557 or Differences in the efficacy of establishing relationships between breast cancer and cadmium exposures as determined by dietary vs. urinary cadmium measures may reflect the observation that urinary cadmium levels are a stronger marker of lifetime exposures to the metal, given cadmium’s half-life of 12–30 years, while dietary exposure levels reflect a shorter term and potentially more variable marker .Prospective studies of women’s dietary intake of cadmium and later diagnosis of cancers demonstrated a significant relationship between higher levels of dietary cadmium exposure and incidence of both endometrial cancers   and postIn young rats, treatment with low doses of cadmium led to an increase in branching and bud formation in mammary tissue, and the induction of several estrogen-associated proteins. Prenatal exposure of rats to cadmium led to early onset of puberty and greater numbers of mammary terminal end buds, both known risk factors for breast cancer .Estrogenic effects of cadmium have been studied in some detail, and the metal has been shown to interfere with a number of normal estrogen-sensitive pathways : cadmiumIn addition to hormone-mediated effects, cadmium may also promote the development of cancer through epigenetic processes including changes in DNA methylation patterns as well as possible modifications of gene-associated histones .Like several other estrogen-mimicking endocrine disruptors, cadmium interferes with the efficacy of a common chemotherapeutic agent often prescribed for women who have been diagnosed with breast cancer. In a study examining the effects of cadmium, 5-fluorouracil (5-FU), and the two combined on subcellular structure and metabolic activity in cultured MCF-7 breast cancer cells, co-administration of cadmium negated the anti-cancer effects of 5-FU .Section summary: The growing literature on exposures to EDCs, especially early in development, indicates an increased risk of developing breast cancer following exposure to many of these compounds, either alone or in combination. The most substantial human epidemiological data supporting this relationship come from prospective studies on women exposed to DDT during gestation or early childhood and increased development of premenopausal breast cancer [t cancer , 104. ThThe prevailing evidence against synthetic estrogens must also be understood alongside evidence about the effects of plant estrogens (phytoestrogens) on risk for developing breast cancer. While most of the research in this area has focused on possible protective associations with soy-based isoflavones in a normal dietary regime, a growing literature is also examining the potential protective effects of the lignans, enterolactone and α-linolenic acid.Mycoestrogens  can contaminate agricultural and meat products, and this contamination may increase susceptibility to developing breast cancer. Also, exposures to growth enhancing compounds given to meat-producing and dairy animals have been linked to increased risk for developing breast cancer. This section explores the complicated profiles of exposures to food-based estrogens and risk for developing breast cancer. There has been no dermination on potential carcinogenicity of these substances by IARC or NTP.Foods such as whole grains, dried beans, peas, fruits, broccoli, cauliflower and especially soy products are rich in phytoestrogens. While most of the research in this area has focused on possible associations with soy-based isoflavones. Additionally, there is also a growing literature is also examining the possible role of the lignans, including enterolactone and α-linolenic acid, in affecting breast cancer risk.Lignans are polyphenolic compounds found widely in seeds and grains common to a Western diet. They are rapidly metabolized in the gut to the estrogenic compounds, enterolactone and enterodiol .A matched case-control study of mainly premenopausal women in the Nurses’ Health Study II cohort found no overall relationship between plasma enterolactone levels and breast cancer risk. However, in those women whose follicular circulating estradiol levels were below the median, higher enterolactone was associate with a significant decrease in breast cancer risk  . A meta-A recent examination of possible mechanisms underlying the protective effect of enterolactone used the aggressive, highly invasive MDA-MB-321 human breast cancer cell line. Addition of the lignan to the cell culture led to decreased activity in mRNA levels of several genes associated with cell proliferation, as well as increased retention of mitotic cells in the S-phase, and decreased migration and invasion through interference with the cell cytoskeleton .A systematic review of the literature on associations between α-linolenic acid and risk of breast cancer found significant negative relationships between higher intake of flax, a major source of α-linolenic acid, and both breast cancer incidence  and mortality  . In womeAlthough scientific evidence suggests that soy-derived foods offer nutritional benefits and are associated with healthy diets , 583, thSome of the disparity may be related to type of soy products consumed by individuals. Across Asian and Western diets, soy may be processed in scores of different ways, resulting in up to 100-fold differences in levels of particular phytoestrogens between products  and veryp < .0001) [Several epidemiological studies have shown that regular consumption of soy-based products, or other vegetables high in phytoestrogens, as part of a normal balanced diet can exert a protective influence with regards to later development of breast cancer. This effect has been studied extensively in China where soy intake is a regular part of the cultural diet. There, substantial evidence indicates that higher soy intake in adulthood or in adolescence is associated with a decreased risk of pre-menopausal breast cancer  .p < .02) [For Chinese women who were previously diagnosed with breast cancer, higher consumption of soy in its many forms found regularly in a woman’s diet, was correlated with decreased recurrence of cancer  and longer survival  . Complicp < .02) .On the other hand, in a prospective study of women aged 43 to 55 years who had never been diagnosed with breast cancer but were considered to be at high risk, 6 months of dietary isoflavone  intake was associated with increased proliferation of breast cells. The effect was most pronounced in pre-menopausal women .p = .023 for soy intake and trend p = .046 for isoflavone intake) [A series of reports from Japan looking at the relationship between soy intake and breast cancer risk have found an inverse relationship –595, wit intake) .A study of Asian-American women living in California and Hawaii found significant decreases in breast cancer risk associated with greater soy intake during childhood (RR = 0.40 95% CI = 0.18–.83), adolescence (RR = 0.80 95% CI = 0.59–1.09), or adulthood (RR = 0.76 95% CI = 0.56–1.02) . The proSeveral studies have directly compared effects of consuming culturally appropriate soy diets in Asian and Western women. A 2012 meta-analysis that combined data from six studies found that regular dietary intake of soy during adolescence decreased the incidence of all later breast cancers (OR = 0.82 95% CI = 0.67–0.99), and was particularly effective in decreasing cancer incidence in pre-menopausal women (OR = 0.66 95% CI = 0.55–0.80). There was no reported difference in the effects of dietary intakes of soy during adolescence between Asian and American/European women . On the Data from studies on laboratory animals and cell culture models have indicated a more complicated story. In several studies, exposures to phytoestrogens have led to increases in mammary tumor proliferation and growth. In ACI rats, dietary exposure to total soy isoflavone content from conception through adulthood decreased incidence of mammary tumors in adult animals by 20% and multiplicity by 56%, while also decreasing the latency to tumor onset by 20% and almost tripling tumor volumes . ExposurThe soy phytoestrogens, genistein and daidzein, as well as their metabolites, cause oxidative DNA damage, a process that is thought to play a role in tumor initiation. Other data suggest that these two soy-based phytoestrogens may have opposing effects on the efficacy of the breast cancer drug, tamoxifen , 608.The effects of the phytoestrogens may well be related to the particular components and doses in the diet , and celIsoflavones contained within natural soy flour have different effects than addition of isoflavones purified from the soy flour on gene expression patterns in induced tumors grown from MCF-7 cells in athymic nude mice. When mice were fed isolated isoflavones, the gene expression pattern was similar to that found in mice that had been treated with estradiol, while the pattern in animals treated with isoflavones included within a full soy flour were more like the negative control, suggesting an inhibitory effect of soy flour proteins on some of the proliferative effects of isolated isoflavones . In addiIn cultured MCF-7 cells, the soy phytoestrogen daidzein slightly enhanced cell proliferation in the absence of natural estrogen , while resveratrol (found in grapes and red wine) significantly decreased tumor cell proliferation . These lConcern has been raised about exposure of newborn babies to soy-based products, primarily through infant formulas. Although one study has shown that feeding only soy formula for the first 4 months of life was associated with a decrease in later development of breast cancer , animal Mycotoxins are compounds produced by several fungal species that contaminate agricultural and feed products, including corn silage and hay, both during before harvest and during later storage –619. PeoContamination of food by zearalenone (ZEA) and its natural metabolites has been associated with the development of precocious puberty, a known risk factor for breast cancer, in young girls , 622. OnA case-control study of dogs revealed that higher dietary exposures to mycotoxins (aflatoxin G1 or G2) resulted in a significant increase in the number of mammary tumors  .In rat dams fed diets containing ZEA, both the compound and its metabolites crossed the placental barrier and also appeared in mother’s milk . ExposurRats treated on post-natal days 15–19 with ZEA and then with the carcinogenic substance, N-methyl-N-nitrosurea (MNU), at puberty developed fewer mammary tumors, with lower multiplicity, than matched controls treated only with the NMU carcinogen, although there was no difference in the latency to appearance of tumors in either group .In cell culture models of human breast cancer, mycotoxins including Fusarin C and ZEA and their metabolites have been shown to be estrogenic . For exaThe synthetic compound, zeranol , is a potent non-steroidal growth promoter that mimics many of the effects of the natural hormone estradiol. Zeranol (ZER) is used extensively in the U.S. and Canada to promote rapid and more efficient growth rates in animals used as sources for meat .As with the natural compound ZEA, ZER is a strongly estrogenic chemical as demonstrated by its ability to stimulate growth and proliferation of human breast tumor cells in vitro at potencies similar to the natural hormones, estradiol, and the known carcinogen, diethylstilbestrol (DES) . A 2007 Treatment of young adult female mice with ZER led to increased growth and branching of mammary glands, similar to what is found in mice treated with the natural hormone estradiol . IncreasBrief (4-day) prepubertal exposure of mice or rats to either ZEA or ZER accelerated the onset of puberty, but did not affect development of the mammary gland structures through early adulthood , 637.A series of studies examined estrogenic activity in normal breast epithelial cells and breast cancer cells treated with ZER. Abnormal cell growth was significant even at ZER levels almost 30 times lower than the FDA-established limit in beef . Follow-Despite opposition from physicians, scientists and consumer advocacy groups, the Food and Drug Administration in 1993 approved Monsanto’s genetically engineered hormone product, recombinant bovine growth hormone , for injection in dairy cows to increase milk production . This hoDrinking any type of cow’s milk noticeably raises body levels of insulin growth factor 1 (IGF-1), a naturally occurring hormone in both cows and humans. Injecting cows with rBST leads to an increase in IGF-1 levels in milk , althougAlthough the data are complex with some studies reaching different conclusions, several epidemiological studies have indicated a relationship between dairy consumption and breast cancer risk in pre-menopausal women . ElevateOne mechanism by which IGF-1 may raise risk in younger women is by increasing breast density in pre-menopausal women, a known risk factor for cancer . In addiProponents of rBST argue that IGF-1 is harmless because it occurs naturally in humans, is contained in human saliva and is broken down during digestion. However, animal evidence indicates that digestion does not break down IGF-1 in milk because casein, the principal protein in cow’s milk, protects IGF-1 from the action of digestive enzymes .Section summary: When incorporated into regular nutritious diets, lignans and soy-based foods have been shown to be protective against breast cancer in numerous epidemiological studies. This protection is especially clear when dietary intake begins in childhood. On the other hand, both mycoestrogens and the stock animal growth enhancer zeranol are estrogenic in their interactions with human breast cells, including cells derived from cancers, in cell culture environments. The data are more ambiguous on possible effects of elevated IGF-1 levels, found after drinking cow’s milk.Not all chemicals associated with increased risk for breast cancer exert their effects through endocrine disrupting mechanisms. This section examines the literatures linking a increased risk for developing breast cancer to a few industrial chemicals, all of which have been determined to be carcinogenic by IARC  of benzene will be consumed globally by the year 2020 . ExposurEpidemiological studies of the effects of benzene on breast cancer risk are difficult to conduct, mainly because exposures to benzene occur in conjunction with exposures to other chemicals that are also released in combustion and manufacturing processes. Also, few of the occupational studies focusing on chemical and automotive industries have included women in substantial numbers to draw meaningful conclusions. One study that did look at relevant occupations among female Chinese workers, examined incidence by occupation as standardized by general breast cancer incidence rates in Shanghai and the number of women in each occupation according to the 1982 census. The occupations in which elevated risks for breast cancer were found included scientific research workers (SIR + 3.3); medical workers practicing Western style medicine  or Chinese-Western style medicine ; as well as workers with expected lower exposures such as teachers, librarians and accountants (SIRs 2.3–2.7). In the same study, looking across professions, benzene exposure was associated with an elevated risk of breast cancer . A studyThe largest study implicating benzene and associated chemicals comes from an occupational study looking at men who have been diagnosed with breast cancer. Men who had worked in professions that involved exposures to gasoline fumes and combustion had significantly increased rates of breast cancer. The effect was most pronounced among men who started at their jobs before the age of 40 .Benzene administration to laboratory mice induces mammary tumors. Mice exposed to benzene have frequent mutations of genes that are responsible for suppressing the development of tumors , 664.Manufacturers use polyvinyl chloride (PVC) extensively to produce food packaging, medical products, appliances, cars, toys, credit cards and rainwear. When PVC is made, vinyl chloride may be released into the air or wastewater. Vinyl chloride has also been found in the air near hazardous waste sites and landfills and in tobacco smoke.Vinyl chloride was one of the first chemicals designated as a human carcinogen by the NTP , 666. ViAnimals exposed long-term to low levels of airborne vinyl chloride show an increased risk of mammary tumors .1,3-butadiene is an air pollutant created by internal combustion engines and petroleum refineries. It is also a chemical used in the manufacture and processing of synthetic rubber products and some fungicides. In addition, 1,3-butadiene is found in tobacco smoke.The EPA determined that 1,3-butadiene is carcinogenic to humans, with the main route of exposure being through inhalation. Women working in the synthetic rubber industry who had high exposures to 1,3-butadiene had increased risk of dying from breast cancer (RR = 2.6 m 95% CI = .9–7.3) . The NTPData from research on animals indicate that females may be more vulnerable to the carcinogenic effects of 1,3-butadiene , which iEthylene oxide is a fumigant used to sterilize surgical instruments and is also used in some cosmetic products . EthylenScientists from the National Institute for Occupational Safety and Health (NIOSH) studied breast cancer incidence in 7576 women exposed to ethylene oxide while working in commercial sterilization facilities. They found an increased incidence of breast cancer among these women in direct proportion to their cumulative exposure to ethylene oxide . AlthougStudies in which human breast cells grown in vitro were exposed to low doses of ethylene oxide demonstrated that the chemical exposure resulted in a significant increase in damage to the cells’ DNA . These fSection summary: Epidemiological studies of both men and women exposed occupationally to benzene or vinyl chloride have higher risk for developing breast cancer. Limited human also indicate that exposures to 1,3-butadiene also have an increased risk for breast cancer, while the evidence supporting this relationship is more robust for ethylene oxide.Increasing evidence indicat4es that exposure to the many chemicals included in tobacco smoke, both through active (first hand) and passive (second hand) means, can increase risk for developing breast cancer. We discuss this literature in this section. While exposures to smoke are often clustered with alcohol consumption and other lifestyle factors, in this category we only focus on tobacco smoke exposures as these are from chemicals polluting the environment, and the exposures are often involuntary.Tobacco smoke contains polycyclic aromatic hydrocarbons (PAHs), as well as hundreds of other chemicals , includiA large study of California teachers revealed an increased risk of breast cancer among smokers, particularly those who began smoking during adolescence , at least 5 years before their first full-term pregnancy , or who were longtime or heavy smokers  . SeveralResults from the Canadian National Breast Screening Study indicated that increased incidence of breast cancer was associated with longer duration of smoking , number of cigarettes smoked per day , and cumulative exposure to cigarette smoke  . SimilarAlthough several more recent studies have reported that beginning smoking before a first full-term pregnancy (independent of age of onset of smoking) may make a woman increasingly susceptible to later diagnosis with breast cancer , 697, a A population-based case control study examined effects of active smoking and risk of developing breast cancer based on whether tumors were luminal (ER+ and/or PR+) or basal  types. Ever smoking led to an increased risk of developing luminal-type cancer , but not basal-type, an effect that was most pronounced in Black women. Another study looking at inflammatory breast cancer incidence reported effects of active smoking on luminal , but not other types of breast cancer . HoweverEthnic differences were reported in a study of Mexican and U.S. non-Hispanic white women. For Mexican women, a significant increase in breast cancer risk was found for former smokers , and this effect was increased for former smokers with a history of alcohol consumption . For U.S. non-Hispanic white women, current smoking of more than 20 cigarettes a day was associated with increased risk . There were no significant effects found for U.S. Hispanic white women .p < .03) [A prospective cohort study of 186,150 female AARP members, 7486 of whom developed breast cancer, found an increased risk of developing breast cancer in current active smokers  as well as former active smokers . For current smokers, the effect was significant in women with no family history of breast cancer , but not in women with a family history. Later age of menarche was also associated with higher risk for developing breast cancer in active smokers  .Several recent studies have examined the effects of smoking at the time of breast cancer diagnosis and subsequent outcomes. Bérubé reported that smoking at the time of diagnosis led to an increase in all-cause mortality, as well as a significant increase in mortality from breast cancer  . SimilarIn 309 female ER+ breast cancer patients being treated with aromatase inhibitors, smoking before surgical treatment for their disease was associated with increased numbers of breast cancer events , distant metastases , and mortality . There was no relationship between smoking and breast cancer-related outcomes in women undergoing other forms of adjuvant therapy .p < .001). Similar effects were found for both White (but not Black) and non-Hispanic (but not Hispanic) men [Two recent studies have examined smoking status and breast cancer outcomes in men. In a pooled case-study consortium with 2378 cases of male breast cancer in Florida, Cook et al. found no evidence of association between smoking status, pack-years, duration, or age at initiation of smoking and risk of developing breast cancer . Anothernic) men .p = .009) [In addition to effects of active smoking on breast cancer incidence and mortality, a growing literature implicates exposures to second hand smoke (passive smoking) to increased risk for the disease. Until recently, more evidence linked secondhand smoke than active smoking to breast cancer risk. Current evidence suggests that both exposures increase breast cancer risk by about the same amount, even though women who are exposed to secondhand smoke receive a much lower dose of carcinogens than do active smokers , 714. Re = .009) .A meta-analysis of eight studies of Chinese women exposed to passive smoking who were never active smokers themselves showed a significant increase in risk of developing breast cancer  . A more NAT2) phenotype [BRCA1 [CYP1A1 and COMT [In trying to understand the mechanisms by which active and/or passive smoking might affect risk for developing breast cancer, several gene expression studies have been conducted. Studies exploring links between smoking and breast cancer incidence, recurrence and mortality have identified several polymorphisms associated with increased risk. The most consistent data implicate a ‘slow acetylator’ n-acetyltransferase 2 , examined the association between tobacco smoking and sex hormone levels in post-menopausal women, whose ovaries are no longer the major source of their of circulating hormones. Smoking was related to higher levels of testosterone, estradiol and other steroid hormones . The incSection summary: There is now a substantial literature indicating that past and current active cigarette smoking is associated with a higher risk for developing breast cancer. For women who are smokers at the time of diagnosis, there is also an increased risk in mortality from breast cancer. These effects are complicated by interactions with race/ethnicity, history of alcohol consumption and subtype of breast cancer being evaluated.In 2007, IARC concluded that shift work is ‘probably carcinogenic to humans’ based in large part on the growing association between shift working and increased incidence of breast cancer  see Tab. Severalp = 0.010) was found for increased exposure length  and risk for developing breast cancer [Associations between long-term (> 20–30 years) night-shift work and breast cancer were reported in a 2008 comprehensive review of 13 studies . Four ott cancer . On the t cancer . A more t cancer .A record linkage study of occupation and cancer in Britain calculated that for 2012, the population attributable factor (PAF) of night shift work may account for 4.5% (95% CI = 3.2–5.9) of breast cancer diagnoses  and deaths  . A similIn a study of Danish nurses, effects of night shift work on breast cancer risk were greatest for women who worked rotating hours that include the overnight, as opposed to evening shift  and for those who worked 12-h shifts that alternated day and night work, as compared to shorter work periods  .Risk of developing breast cancer increased for women who worked night shifts for more than 4.5 to 5 years , and for those who regularly engaged in night work for at least 4 years prior to their first pregnancy , therefore before the time when their mammary cells had fully differentiated .The most thoroughly studied mechanism to explain these effects of night shift work is the light-at-night (LAN) hypothesis . IncreasClinical studies have demonstrated that there is a decrease in the peak amount of melatonin secreted in women with metastatic cancer, as compared with healthy women, and larger tumors are associated with lower levels of melatonin . Blind wOne proposed pathway by which reduced melatonin might affect breast cancer risk is enhancement of the production or secretion of estradiol and other ovarian hormones. Nagata et al. reported that postmenopausal women who worked night shifts that went beyond midnight had significantly increased serum concentrations of estradiol both during their night shift phases and when they rotated to regular day awake periods, as compared with controls who did not engage in late night shift work . Davis eIn rodent models, higher levels of melatonin are associated with decreased incidence and size of mammary tumors, and when they do occur, the latency period of tumor development is lengthened . In humaPer3, is associated with higher breast cancer rates in young women [Per2, another gene associated with the control of daily rhythms, is also poorly regulated in many women with breast cancer, with normal structure and expression of this gene being associated with lower effectiveness of estradiol in altering cellular activity. In healthy cells, Per2 also may act directly as a tumor-suppressor gene, decreasing the activity of pathways associated with tumor formation [CLOCK gene has been associated with an increased risk for developing breast cancer , and there was a positive interaction between the presence of this genotype and night shift work on risk for developing breast cancer (p = .02) [Mechanistically, night pulses of melatonin enhance the activity of endocrine, metabolic and immune-related pathways that can prevent the development of cancer . These png women . Per2, aormation . A rare p = .02) . Howeverp = .02) .Other recent studies have greatly complicated the light-at-night and breast cancer story. Relationships between night shift work and melatonin levels may be mediated by race/ethnic background. In a large population-based study of Chinese women, no association between shift work and breast cancer incidence was reported . Asian aSeveral authors have proposed that factors associated with night shift work, beyond decreases in melatonin levels, need to be considered in understanding better the links with increased risk for breast cancer. Other possible consequences of shift work, including phase shift sleep disruption, lifestyle factors, changes in metabolism, desynchronization between central neural and peripheral systems, or decreased vitamin D production, may also be linked to increased cancer rates. These factors need to be studied as both single and possibly interacting factors in altered risk for developing breast cancer –762.Finally, as with several endocrine disrupting chemicals, light-at-night decreases significantly the effectiveness of major chemotherapeutic agents used in the treatment of breast cancer. In rat models with MCF-7 breast cancer cells xenografts, addition of dim light exposures during the dark phase of the cycle led to decreased melatonin secretion during the dark phase, decreased latency to tumor progression, increased tumor growth, and complete resistance to both tamoxifen and doxorubicin , 764.Section summary: Extensive experience with night shift work, and therefore higher exposure to light-at-night (LAN), has been shown to increase risk for breast cancer, although there may be ethnic differences in this response. The most studied underlying mechanism for the effect of LAN exposures is the accompanying change in patterns of melatonin secretion. Other lifestyle and physiological factors associated with shift work have also been proposed to alter risk for developing breast cancer.Exposure to ionizing radiation, from both military and medical sources, is the best known and longest established environmental cause of breast cancer in both women and men. Exposures early in life, during childhood through adolescence, are particularly important. Data for potential links between electromagnetic fields, or non-ionizing radiation, and breast cancer are mixed and inconclusive.Ionizing radiation is any form of radiation with enough energy to break off electrons from atoms (to ionize the atoms). This radiation can break the chemical bonds in molecules, including DNA molecules, thereby disturbing their normal functioning. X-rays and gamma rays are the only major forms of radiation with sufficient energy to penetrate and damage body tissue below the surface of the skin.Among the many sources of ionizing radiation are traditional X-rays, computed tomography (CT) scans, fluoroscopy and other medical radiological procedures. Sources of gamma rays include emissions from nuclear power plants, scientific research involving radionuclides, military weapons testing and nuclear medicine procedures such as bone, thyroid and lung scans .In 2005, the National Toxicology Program classified X-radiation and gamma radiation as known human carcinogens   are more likely to develop breast cancer and may be especially susceptible to the cancer-inducing effects of exposures to ionizing radiation [er women . In addiadiation , 783–785Studies using animal and in vitro human breast tumor cell culture models have demonstrated that the effects of radiation on mammary carcinogenesis may be additive with effects of estrogens –788. ThiP = .01) for correlation with earlier year beginning work. Technologists who began working before 1950 and had worked for at least 5 years had an increased mortality rate from breast cancer  [Female radiology technologists who had sustained daily exposures to ionizing radiation demonstrated an increased risk of breast cancer for those women who began working during their teens or, independent of age, working in the field before the 1940s, when exposure levels were substantially higher than they have been in more recent decades , 790. Fo95–6.68) . In a su95–6.68) . The sus95–6.68) .A review and analysis of all existing related studies found that women who work as airline flight attendants had increased levels of breast cancer . A meta-Medical X-rays: Use of X-rays to examine the spine, heart, lungs, ribs, shoulders and esophagus also exposes parts of the breast to radiation. X-rays and fluoroscopy of infants irradiate the whole body [ole body . Decadesole body , benign ole body , 107, acole body , enlargeole body , 110, skole body , scoliosole body , Hodgkinole body –116, nonole body , acne [1ole body , and proole body .BRCA1/2 gene mutations is associated with an increased risk of breast cancer  [Anytime use of diagnostic chest X-rays before the age of 50 years in women carrying the 62–2.42) .p < .001) [Evidence from almost all conditions suggests that exposure to ionizing radiation during childhood and adolescence is particularly dangerous with respect to increased risk for breast cancer later in life , 126 and < .001) . Importa < .001) , 800.Computed Tomography (CT) Scans: There is credible evidence that medical X-rays  are an important and controllable cause of breast cancer [t cancer , 801. Alt cancer , 803. Int cancer . When a t cancer . Modelint cancer . Other mt cancer .CT angiography, a source of comparatively high radiation to the chest, has been associated with a significant increase in risk for developing breast cancer, especially in pre-menopausal women , 808.Mammography: Many experts believe that the low-dose exposures to radiation received as a result of mammographic procedures are not sufficient to increase risk for breast cancer. However, damage from lower-energy sources of X-rays, including those used in mammography, cannot be predicted by estimating risk from models based on higher doses [er doses , 809. Ever doses .As with other risk factors for breast cancer, both age at exposure and the individual’s genetic profile influence the degree of increased risk for disease in women exposed to multiple mammograms. For example, women who had multiple mammograms more than 5 years prior to diagnosis had an increased risk for breast cancer, but the effect was only statistically significant for women whose first mammograms began before age 35 .BRCA mutations, begin annual mammography screening at age 25 to 30. But, young women with these mutations are actually more vulnerable to the cancer-inducing effects of early and repeated mammograms. This increased vulnerability has been reported in women with BRCA1/2 mutations [BRCA2 mutations, meta-analysis of seven articles found low-dose exposures from either mammography or chest X-rays led to an increase risk for breast cancer . Exposure before the age of 20 increased risk , as did greater than 5 years of exposures  [This age effect is of particular concern, as it is often recommended that high-risk women, including carriers of either of the utations , 72 as wutations . For wom1.1–3.0) . Diagnos1.1–3.0) .The detrimental risks from mammography might also be heightened in older women, whose breast epithelial cells have gone through several decades of cell division. Cells derived from older women’s breast tissue were more sensitive to the DNA-damaging effects of low-energy radiation, increasing the likelihood of later conversion to cancerous cells .In 2009, the U.S. Preventive Services Task Force (USPSTF) recommended against the use of routine mammography screening before the age of 50 , and ever treatment with radiotherapy , but no significant interaction between the two factors [More recent data indicate that women younger than 45 who received the higher radiation exposure associated with post-lumpectomy radiotherapy (as compared to post-mastectomy radiation) had a 1.5–2.5-fold increase in later contralateral breast cancer diagnoses. This effect was especially prominent in younger women with a substantial family history of breast cancer –826. Ber factors .Electromagnetic waves are a type of low frequency, non-ionizing radiation without enough energy to break off electrons from their orbits around atoms and ionize the atoms. Microwaves, radio waves, radar and radiation produced by electrical transmission are examples of radiation sources that generate electromagnetic fields (EMF). Fluorescent lighting, computers and many other types of wired and wireless electronic equipment  all create electromagnetic fields of varying strengths.Both IARC and the National Institute of Environmental Health Sciences (NIEHS) EMF Working Group have classified EMF exposures as a possible human carcinogen based on the scientific literature related to EMF and childhood leukemias . More reAlthough many epidemiological or occupational studies have not found significant relationships between exposures to EMF and risk for breast cancer, others have reported data supporting these effects , 830. MeKliukiene et al. reported an increased risk of breast cancer among Norwegian female radio and telegraph operators exposed to radiofrequency (one type of EMF) and extremely low frequency EMF. Pre-menopausal women showed an increased risk of estrogen-receptor-positive tumors  and post-menopausal women had an increased risk of estrogen-receptor-negative tumors  .In an occupational study that looked at women in job setting with the potential for high, medium or low electromagnetic exposures, high exposures were associated with an increased risk for developing breast cancer . Pre-menopausal women appear to be at higher risk  than post-menopausal women  .Studies of residential and occupational EMF exposure found a significant increase  in breast cancer risk among women of all ages living near high-voltage power lines. Similar effects were found for women with ER+ and ER– tumors. Occupational exposure also increased risk  . Women yNevertheless, meta-analyses of 15 studies concluded that there is no clear relationship between EMF exposure and breast cancer in women  . AnotherAlthough breast cancer is rare in men, numerous occupational exposure studies point to a connection between EMF exposure and male breast cancer –842.In the laboratory, EMF can cause increased mammary tumors in animals and proliferation in systems in which human breast cell tumors are grown in culture. Importantly, effects in rodents are found in some strains of animals but not others, indicating that subtle differences in genetic background might make some animals more susceptible to the carcinogenic effects of EMF . In an iSection summary: Exposure to ionizing radiation is a known cause of increased risk for breast cancer. Victims of military use of nuclear bombs have increased risk, as do women who had X-ray treatments for medical purposes, especially when they were young. Women carrying the BRCA1/2 mutations are particularly susceptible to the effects of X-rays, including those emitted by routine mammography.More mixed results come from studies of women exposed to non-ionizing radiation, either because of occupational or residential exposures.In the 8 years since we last published an extensive review of the relevant literature, hundreds of new papers have appeared addressing the link between exposures to environmental toxicants and an increased risk for developing breast cancer; the majority of the studies support the existence of this link for the agents discussed in this review. Not only has the corpus of the literature expanded in size over the past several years, but it has also been enhanced by greater depth, breadth, and complexity. The growing literature on developmental exposures to EDCs and later development of breast cancer is especially strong.Epidemiological data strongly support the link between increased risk of developing breast cancer and early developmental exposures to DES, DDT and radiation, as well as adult exposures to oral contraceptives and HRT. A growing literature also implicates engaging in night shiftwork as an important factor leading to increased risk for breast cancer. On the other hand, a substantial literature examining the effects of consuming soy products and lignans as part of a regular diet, especially starting early in life, indicates they can have a protective effect against later development of breast cancer.Animal and other in vitro models support the hypothesis that many other chemicals found in commonly used consumer products, as well as in our air, water and dust, all are associated with increased risk for predisposing mammary tissue to develop tumors. These data support the strong links described above for EDCs. Data from epidemiological studies suggest connections between exposures and later development of cancer, although methodological limitations often constrain the conclusions that can be drawn. Of particular concern for most epidemiological studies in this field is the lack of direct measurement of toxicant exposure levels in individuals, especially in the years (or decades) prior to diagnosis of the breast cancer . As the Importantly, through animal, cell culture, high throughput and other non-epidemiological models, mechanisms are being elucidated by which exposures to various toxicants may lead to increased risk for developing cancer. This literature has been slow to develop, because regulatory toxicological studies examining reproductive and developmental consequences of exposures to various drugs or potential toxicants have not required examination of mammary tissue endpoints . There aDespite these critical methodological limitations and concerns, the breadth and strength of the evidence cited in this review, when taken as a whole, reinforce the conclusion that exposures to a wide variety of toxicants – many of which are found in common, everyday products and byproducts – can lead to increased risk for development of breast cancer. As concluded by the reports of the Presidential Cancer Panel  and the


Risk prediction models can best be developed in prospective longitudinal cohort studies, as such studies allow optimal measurement of predictor and outcome variables and direct estimation of absolute risk . ProspecKarp et al  propose The main issue is the selection process of the cases and controls. A major limitation of case-control studies, described as early as 1959, is the difficulty to ensure that cases and controls are a representative sample of the same source population . By weigThe weighting greatly affected the model intercept, which is expected, as only 1,288 controls were included in the matched case-control study from over 3 million controls in the Montreal population. Moreover, the odds ratios changed for age (from 1.1 to 3.4 per decade) and gender . These changes in parameter estimates are also expected since the weighting is meant to correct for the age- and sex-matching of cases and controls. However, the odds ratio for the comprehensive smoking index (CSI) changed drastically as well: from 10.1 to 31.5. This illustrates that the weighting can substantially affect the parameter estimates of risk factors other than the ones used to match the cases and controls.Finally, the authors state that the risk-stratifying performance of their method was “reasonably high”, based on assessing the range and variability of 15-year lung cancer risk across a variety of risk profiles . We noteWe hence agree with the authors that an external validation study of the weighted model in a population where the level of absolute risk is known is essential . Such a


Circulating osteoprotegerin (OPG), a member of the receptor activator of nuclear factor kappa-B (RANK) axis, may influence breast cancer risk via its role as the decoy receptor for both the RANK ligand (RANKL) and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Circulating OPG and breast cancer risk has been examined in only one prior study.n = 1622; ER–, n = 386), matched 1:1 to controls, were included in the analysis. Women were predominantly postmenopausal at blood collection (77%); postmenopausal women included users and non-users of postmenopausal hormone therapy (HT). Serum OPG was quantified with an electrochemiluminescence assay. Relative risks (RRs) and 95% confidence intervals (CIs) were calculated using conditional logistic regression.A case-control study was nested in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort. A total of 2008 incident invasive breast cancer cases (estrogen receptor (ER)+, ptrend = 0.03). We observed a suggestive inverse association for ER+ disease overall and among women premenopausal at blood collection. Results for ER– disease did not differ by menopausal status at blood collection (phet = 0.97), and we observed no heterogeneity by HT use at blood collection (phet ≥ 0.43) or age at breast cancer diagnosis (phet ≥ 0.30).The associations between OPG and ER+ and ER– breast cancer differed significantly. Higher concentrations of OPG were associated with increased risk of ER– breast cancer  contains supplementary material, which is available to authorized users. Osteoprotegerin (OPG) is a homodimeric glycoprotein and a member of the tumor necrosis factor (TNF) receptor superfamily . OPG wasBesides bone, OPG is expressed in other tissues, including the stomach, intestines, skin, liver, heart, lung, kidney, and breast. This expression across diverse tissue types indicates that its biologic functions may extend beyond bone metabolism. In relation to breast cancer, OPG was initially investigated as a potential inhibitor of metastasis-related osteolysis , 4. The n = 76), risk by tumor subtypes  and progesterone (PR) receptor status) was not investigated. We provide the first prospective data on OPG and breast cancer risk by hormone receptor status, in a large nested case-control study in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort.Besides local expression in many tissue types, OPG is present in blood. Circulating OPG has been examined in the context of chronic disease risk, including impaired glucose tolerance and type 2 diabetes , vasculan = 367,993 women), from 10 European countries , generally between ages 35 and 75 years, enrolled in the study. Detailed dietary, anthropometric, lifestyle, and medical history data were collected via standardized methods. Blood samples were collected according to standardized protocols . Samples for this study were stored centrally under liquid nitrogen (–196 °C) at the International Agency for Research on Cancer (IARC), except those from Denmark, which were stored locally at –150 °C.The EPIC cohort was designed to identify risk factors for cancer . BrieflyIncident cancers were identified through linkages with regional cancer registries except in France, Germany, Greece, and Naples , where follow-up is conducted by review of health insurance records, contacts with cancer and pathology registries, and/or direct contact with cohort members. Vital status is ascertained through linkages with regional and national mortality registries and active follow-up (Germany and Greece). Details on the identification and verification of incident breast cancer cases and collection of hormone receptor status data were reported previously .Case and control selection has been described previously . Cases aThe end of follow-up for this study was the last date of complete follow-up for both cancer incidence and vital status . All incident cases with ER status available were included through 2004. After 2004, all newly diagnosed ER– cases were included, and among postmenopausal women an equal number of ER+ cases were randomly selected among cases matching each ER– case for recruitment center.One control per case was selected among cohort members who donated a blood sample and who were alive and free of cancer (except non-melanoma skin cancer) at the time of invasive breast cancer diagnosis of the index case. Controls were matched to cases on recruitment center, age (±3 months), menopausal status, HT use, fasting status , and time of day (±1 hour) at blood donation. Premenopausal women were also matched for phase of menstrual cycle .n = 7 sets) or had OPG values identified as outliers (n = 5 sets), a total of 2008 case-control sets remained for analysis. PR status was available for a total of 74% of cases (n = 1480).A total of 2020 case-control sets were initially selected. After excluding sets in which the case or control was missing the OPG measurement (The EPIC-Heidelberg cohort was recruited between 1994 and 1998. The EPIC-Heidelberg substudy has been described previously . BrieflySerum OPG concentrations were measured in the Laboratory of the Division of Cancer Epidemiology at the German Cancer Research Center (DKFZ), using an electrochemiluminescence assay . Samples from cases and their matched controls were analyzed in the same analytical batch, and laboratory personnel were blinded to the case-control status of the samples. The precision of the laboratory work was monitored by inclusion of blinded pooled quality control (QC) samples (two per batch). Intra-batch coefficients of variation (CVs) were 15%; inter-batch CVs were 17%.Serum concentrations of estradiol, estrone, testosterone, dehydroepiandrosterone sulfate (DHEAS), sex hormone-binding globulin (SHBG), progesterone, prolactin, and insulin-like growth factor 1 (IGF-1) were available for subsets of the study population and were assessed as covariates and effect modifiers. Laboratory methods have been described previously , 17, 18.OPG was log2-transformed to obtain an approximately normal distribution; this transformation allows an estimation of the effect of a doubling of biomarker concentration. Outliers were evaluated using the extreme Studentized deviate many-outlier procedure .Spearman correlations were used to evaluate associations between OPG and continuous covariates and endogenous hormones; geometric means of OPG were compared between categories of categorical covariates. These analyses were restricted to controls and adjusted for matching factors. OPG was classified into tertiles based on the distribution in controls. As OPG levels do not vary significantly by menopausal status, tertile cut-off points were calculated based on the overall control population. Conditional logistic regression was used to estimate the relative risk (RRs) and 95% confidence intervals (CIs). Tests for trend were based on OPG modeled as a continuous variable. OPG concentrations are known to increase with age; therefore, Spearman correlations were used to examine the reproducibility of the relative ranking of study subjects over time, comparing concentrations in samples taken 1 and 14 years apart.2) were included in the multivariable model. Additional adjustment for lifetime mean alcohol consumption, past oral contraceptive use, breastfeeding, and smoking status did not materially impact the results (RRlog2 change <10%).Ages at menarche, menopause, and first full-term pregnancy (FTP), number of FTPs, and body mass index , with the exception of the association between OPG and ER+ breast cancer among women premenopausal at blood collection (p = 0.03). Finally, we performed sensitivity analyses after excluding breast cancer cases diagnosed within 2 years of blood collection  to address potential reverse causation.We evaluated heterogeneity by reproductive and lifestyle factors or endogenous hormone levels by comparing models including and excluding interaction terms using the likelihood ratio test (LRT). Tests for interaction were based on continuous, log2-transformed OPG concentrations. We assessed potential heterogeneity by tumor hormone receptor status and age at diagnosis (<50 vs. 50+ years) by comparing models assuming the same association between OPG and breast cancer in subgroups  to one assuming different associations by subgroup using the LRT . We examp < 0.05 level. SAS 9.3  was used for all statistical analyses.All statistical tests were two-tailed and significant at the th–90th percentiles: 45–64) years, and among cases the median age at diagnosis was 61 (10th–90th percentiles: 50–70) years. Median time between blood collection and diagnosis was 4.7 (10th–90th percentiles: 1.2–8.1) years. Of the 2008 total cases, 81% were ER+ .A total of 462 (23%) case-control pairs were premenopausal at blood donation, whereas 1546 pairs were postmenopausal . Among premenopausal women, OPG did not vary by menstrual cycle phase (p = 0.29). OPG concentrations did not vary by menopausal status at blood collection (p = 0.31). However, among women postmenopausal at blood collection, OPG levels differed between current users and non-users of HT , although the absolute differences were small . Among HT users, OPG levels did not further differ by type of HT .Serum OPG concentrations were positively correlated with age (2), or alcohol consumption (g/day), nor did concentrations differ between women with and without completed FTP (data not shown). Higher OPG concentrations were observed in women reporting ever OC use, as compared to never users . Among women with additional hormone measurements available (n: 297–2008) OPG was not correlated (r < |0.14|) with endogenous sex steroid hormones, IGF-I, or prolactin, among either pre- or postmenopausal women, or within strata of postmenopausal HT users and non-users  (Table ptrend = 0.03). In contrast, we observed a suggestive inverse association between OPG and ER+ disease . The association between OPG and ER– disease did not differ by menopausal status (phet = 0.97). However, we observed suggestive heterogeneity by menopausal status for ER+ disease ; postmenopausal, RRlog2 = 0.97 [0.75–1.25]; Table p = 0.03; Additional file phet ≥ 0.43) or by age at breast cancer diagnosis  and heterogeneity by testosterone concentrations for ER+ disease . Finally, results were similar in sensitivity analyses restricted to women diagnosed >2 years after blood collection. OPG demonstrated high within-person reproducibility, in terms of the relative ranking of study participants, over 1 year (r = 0.85) and 14 years (r = 0.75).We observed no evidence for effect modification by other reproductive and lifestyle factors  or by levels of endogenous hormones , with the exception of suggestive heterogeneity by prolactin concentrations for ER– disease  concentrations were associated with an increased risk of ER– breast cancer, and a modest, suggestive reduction in risk of ER+ tumors, in this large investigation. With a total of 2008 breast cancer cases with documented ER status, this is the first large-scale prospective study to address circulating OPG and subsequent breast cancer risk by hormone receptor subtype.BRCA1/2 carriers, higher serum OPG concentrations were associated with lower risk mutation site [n = 18 cases) [BRCA1/2 mutation status was not available in our study population, and family history of breast cancer is missing for the majority of participants (64%). Therefore, we were unable to evaluate OPG and breast cancer risk restricted to a higher risk population in our study. These three investigations used ELISA assays, while we used an electrochemiluminescence assay. Vik [Vik et al. reported an inverse association between OPG concentrations and breast cancer risk in a case-cohort study of more than 6000 women and men (median 13.5-year follow-up) . This Noion site  and lowe8 cases) . BRCA1/2say. Vik  and Odensay. Vik  observedsay. Vik  did not n = 1941), but not among patients with ER– disease (n = 649) [Prior investigations show high levels of OPG protein or mRNA in a variety of breast cancer cell lines , 24–27, n = 649) . These oWe observed increased risk of ER– (and ER–/PR–) breast cancer among women with higher serum OPG concentrations. OPG binding to TRAIL represents one key mechanism through which OPG could promote breast tumor development, particularly of ER– tumors , 38. TRAWe observed a suggestive inverse association between OPG and ER+ breast cancer. OPG may reduce breast tumor development through binding to RANKL. In addition to regulating bone turnover, RANK and RANKL mediate progesterone- and prolactin-induced changes in the mammary gland, including the expansion of mammary epithelial stem cells , prolifeBreast cancer risk increases with higher lifetime number of menstrual cycles, an indicator for cumulative exposure to luteal phase progesterone levels, and is also increased among postmenopausal women using combined estrogen-plus-progestin HT –52. InteWhile several tissue types produce OPG, bone marrow cells and vascular endothelial cells may be the predominant sources of circulating OPG –57. EstrIn summary, recent research has revealed intriguing parallels in the roles for OPG and the RANK/RANKL axis in bone metabolism and in mammary gland physiology. Our large-scale investigation is the first to document potentially diverse associations of OPG with risks of ER– or ER+ breast cancer. There is increasing interest in denosumab — a humanized antibody that blocks RANKL signaling, which is used routinely to treat osteoporosis — as a drug for preventing breast cancer recurrence among women with early stage breast cancer and primary prevention in high risk women . Althoug


The aim of this multicenter, retrospective, case-control study was to identify differences in risk factors of malignancy between men and women with type 2 diabetes.Among women the most prevalent malignancies were: breast and uterine cancers (35.6% and 14.4% respectively), while among men there were: colorectal and prostate cancers (24.5% and 13.3% respectively). In both gender metformin use was associated with lower cancer risk. Obesity and insulin treatment in dose-dependent and time-varying manner were associated with significantly increased risk of malignancy in females. In men, unexpectedly, cardiovascular disease was more prevalent in control group. Other variables did not show significant association with malignancy risk.118 women and 98 men with type 2 diabetes mellitus who developed cancer after diagnosis of diabetes and the same number of strictly age matched controls with type 2 diabetes and without malignancy were included into the study. Diabetes duration, antidiabetic medications use, glycated hemoglobin level, body mass index, smoking habits, occupation, presence of comorbidities and aspirin use were included into analyses.Metformin demonstrated protective effect against cancer in both sexes. Obesity and insulin treatment seem to have greater impact on cancer risk among women. The interest of scientific world in the relationship between diabetes and cancer has a long history , 2. MetaAntidiabetic medications have been long assumed to be able to modulate risk of malignancy. There is increasing evidence indicating protective role of metformin in cancer development and outcomes, which was summarized in several meta-analyses –20. ConvSince in the vast majority of published studies risk of malignancy in T2DM has not been analyzed separately for each gender, it is therefore difficult to assess to what extent risk factors of cancer in this population are gender related. Thus, the main objective of the continuation of our multicenter, retrospective, case-control study  was to aCharacteristics of case and control groups separately for each gender is presented in Table 1c level was not significantly different between the case and control groups, regardless of gender , but it did not attain statistical significance, P = 0.054. Among women this relationship was even less pronounced. Overall impact of glycated hemoglobin on cancer risk was discussed in details elsewhere [1c levels were related to elevated risk of colorectal, pancreatic, respiratory and female genital tract cancers, while they were not related to risk of breast, gastrointestinal or urological cancers [1c level compared to women with other cancer sites . In males this difference, although apparent (HbA1c 7.53 ± 1.30% vs. 7.10 ± 0.98% respectively), it did not attain statistical significance. In a rare study analyzing HbA1c level and cancer risk separately for men and women no association was found among male subjects, while in female patients relationship was significant, but non-linear [Mean HbAnd Table . Among m% Figure . Male sulsewhere . In a re cancers . In our n-linear .1c within a normal range [1c ≥ 8.5%. Statistical significance was not reached, likely due to a small number of patients with such poor metabolic control. However, not only prolonged hyperglycemia, but also acute glucose level fluctuations, frequently seen in diabetic patients, can lead to increased ROS formation [Although increased risk of malignancy was found also in higher versus lower values of HbAal range , it can al range –30. Prolal range , 32. It ormation .Duration of diabetes did not differ significantly between patients with and without malignancy, both among women and men Table . Also whEffect of diabetes duration on the risk of cancer remains a matter of controversy. In two large, registry-based, retrospective cohort studies Johnson et al. and Carstensen et al. independently found the highest number of diagnosed cancer early after diabetes onset, both among women and men , 35. Thi2 respectively, P = 0.002. Among men such difference was not observed (BMI 30.6 ± 4.6 vs. 30.5 ± 4.5 kg/m2 respectively).Significantly fewer patients in the case groups were treated with metformin compared to the control groups in both sexes Tables  and 2. TIn the univariate analysis insulin therapy was associated with increased risk of malignancy, but this association was significant only in women. In the multiple logistic regression analysis the risk of cancer related to insulin use decreased to a non-significant level Table .P = 0.062; Table P = 0.033). Similar tendency was observed also among women (50.7% vs. 69.4% respectively), but in this case difference did not reach statistical significance, P = 0.068. With regard to site-specific cancers, treatment with insulin was significantly more prevalent in the subgroup of men with colorectal cancer in relation to their comparators, 16 vs. 8 patients respectively, P = 0.043, and among women with aggregated breast and uterine cancers vs. their comparators, 34 vs. 21 subjects respectively, P = 0.027.Mean insulin dose and mean duration of insulin treatment did not differ significantly between the case and control groups, regardless of gender Table . HoweverSU derivatives in our study appeared to have neutral impact on the cancer risk. For DPP-4 (dipeptidyl-peptidase-4) inhibitors and for acarbose (α-glucosidase inhibitor) odds ratios were not calculated due to a small number of patients treated with these medications, 24 (5.6%) and 32 (7.4%) subjects respectively.Impact of antidiabetic medications on cancer risk has been widely discussed in the last years. T2DM is a progressive disease and requires intensification of treatment over time. Hyperglycemia is the primary driver of these changes, and the final stage of intensification is insulin therapy in different regimens, with or without concomitant oral or injectable medications (glucagon-like peptide 1 agonists or pramlintide). Time of progression to the next step of treatment regimen varies among different patients, and thus a clear impact of antidiabetic medications on cancer risk is difficult to determine.Highly significant reduction of cancer risk among metformin users, consistent among men and women observed in our study is in line with the results of meta-analyses published in recent years, which also demonstrated protective effect of metformin on cancer incidence and mortality –20 irresCurrent evidence from observational studies indicate possible unfavorable effect of insulin therapy on cancer risk in T2DM , 39, 40.Impact of insulin on cancer growth is biologically plausible. Insulin is a potent growth-stimulating hormone, which acts through insulin and IGF-1 receptors , 42, 43.SU use in our study did not show significant relationship with cancer risk regardless of gender. Data from other observations are divergent. Thakkar et al. in their meta-analysis revealed increased cancer risk among SU users in cohort studies, while in case-control studies and randomized controlled trials it was neutral . In a moThe number of patients treated with other antidiabetic medications in our study was too small to determine their relationship with cancer risk.2) was associated with significantly elevated risk of malignancy, OR 1.92 (95% CI 1.14–3.21), P = 0.019 compared to patients with lower BMI, while in men such relationship was not observed . Interestingly, CVD was significantly more frequent in male controls  as long as the drug is well tolerated and no contraindications occur. In addition, insulin therapy in type 2 diabetic patients should be initiated with caution and, if possible, high doses of insulin should be avoided, which is of special importance in women. At least, in insulin treated patients increased oncological vigilance should be maintained in men in the first 5 years of insulin therapy, and in women between fifth and tenth year of insulin therapy. It is also highly reasonable to make strong efforts for weight reduction, especially in women. And finally, deterioration of metabolic control of diabetes should be avoided and increase of HbA1c measurement before or at the time of cancer diagnosis, date of diabetes diagnosis, diabetes treatment, BMI and history of comorbidities available. Compared to our previous publication study group was supplemented by 13 new cases, and finally into this analysis we included 118 women and 98 men with T2DM fulfilling inclusion criteria. The control group consisted of strictly age-matched 118 females and 98 males with T2DM without history of cancer and without known malignancy. Data analysis covered the period from January 1998 to 30 September 2016 (the first and the last eligible patient with cancer). Other details of methodology used in our study were described in our previous publication [Inclusion criteria for “case” group were as follows: cancer diagnosed after diagnosis of type 2 diabetes, at least one HbAlication .t-test or by a Mann-Whitney rank sum test where appropriate. The categorical data were compared using χ2 test. In the second stage patients were divided into subgroups according to BMI , diabetes duration , quartiles of HbA1c level , insulin dose , and duration of insulin treatment . In addition analysis of the subgroups of patients treated with metformin and insulin was performed. For the assessment of the effect of treatment or analyzed risk factors on cancer occurrence OR (odds ratios) and 95% CI  were calculated in univariate and in multiple logistic regression models. For comparison between site-specific cancer distribution in the study group and in the whole Polish population a z-test was used. A P value < 0.05 was considered statistically significant.Statistical analysis of the data was performed using SigmaPlot for Windows version 12.5 , and similarly to our previous study it was performed in 2 stages . In the The study was approved by the institutional Bioethics Committee at the University of Rzeszow  and by the all appropriate administrative bodies. The study was conducted in accordance with ethical standards laid down in an appropriate version of the Declaration of Helsinki (as revised in Brazil 2013) and in Polish national regulations. According to Polish regulations in non-interventional, retrospective, epidemiological studies, where patients’ data are analyzed anonymously, informed consent is deemed unnecessary and it was not obtained.