"In a finding that challenges the conventional wisdom about the risks of some hormones used in menopause httpshealth.nytimes.comhealthguidesdiseasemenopauseoverview.htmlinlinenytclassifier a major government study has found that years after using estrogen httpstopics.nytimes.comtopnewshealthdiseasesconditionsandhealthtopicsestrogenindex.htmlinlinenytclassifieronly therapy certain women had a markedly reduced risk of breast cancer httpshealth.nytimes.comhealthguidesdiseasebreastcanceroverview.htmlinlinenytclassifier and heart attack httpshealth.nytimes.comhealthguidesdiseaseheartattackoverview.htmlinlinenytclassifier. The research part of the landmark Womens Health Initiative study is likely to surprise women and their doctors who for years have heard frightening news about the risks of hormone therapy. But most of those fears are related to the use of a combination of two hormones estrogen and progestin which are prescribed to relieve hot flashes and other symptoms of menopause and have been shown to increase a womans risk of breast cancer. The new findings httpsjama.amaassn.orgcontent.full.pdfhtml reported Tuesday in The Journal of the American Medical Association come from  women in the Womens Health Initiative study who had previously had a hysterectomy httpshealth.nytimes.comhealthguidessurgeryhysterectomyoverview.htmlinlinenytclassifier the surgical removal of the uterus. Nationwide about onethird of women in their s have had a hysterectomy. The Womens Health Initiative was begun in  by the National Institutes of Health httpstopics.nytimes.comtopreferencetimestopicsorganizationsnnational_institutes_of_healthindex.htmlinlinenytorg as a sweeping investigation of hormone use and other health issues of postmenopausal women.  While most women in the hormone study were taking combination hormone therapy women without a uterus took estrogen alone or a placebo for about six years and were followed for nearly  years. The estrogenonly group was not given progestin which is prescribed only to protect the uterus from the harmful effects of estrogen. Although all the women in the estrogen study stopped using the treatment in  the investigators have continued to monitor their health as is typical in large clinical trials. The most surprising new finding relates to breast cancer. The women with hysterectomies who used estrogen alone had a  percent lower risk for breast cancer compared with those who had taken a placebo. This is in stark contrast to the higher risk of breast cancer shown in the estrogenprogestin part of the trial. The decreased risk of breast cancer in this group is something we totally didnt expect when we started the W.H.I. hormone therapy trials said Andrea Z. LaCroix the studys lead author and a professor of epidemiology at the Fred Hutchinson Cancer Research Center in Seattle. This study differentiates estrogen alone from estrogen and progestin in a very big way. I hope it gets across to women because we are not reversing ourselves. Indeed the investigators emphasized that the results do not change recommendations concerning combination hormone therapy for the twothirds of menopausal women who still have a uterus. The Womens Health Initiative data have consistently shown that the combination of estrogen and progestin raises breast cancer risk and that the treatment should be used only to relieve severe menopause symptoms using the lowest dose for the shortest possible time. But the data are reassuring for millions of middleaged women without a uterus who take estrogen to relieve hot flashes and other menopause symptoms. An accompanying editorial httpsjama.amaassn.orgcontent.extract in the journal was skeptical about the results arguing that the design of the initiative which is skewed toward older women and stopped all forms of hormone treatment after several years of use does not match the way doctors typically prescribe treatment to women in their s at the onset of menopause. Dr. Graham Colditz an author of the editorial and professor of surgery at Washington University httpstopics.nytimes.comtopreferencetimestopicsorganizationswwashington_universityindex.htmlinlinenytorg School of Medicine in St. Louis said he thought data collected from observational studies that show a higher risk of breast cancer associated with estrogen use were more reliable than the data gathered from the Womens Health Initiative clinical trial. The finding doesnt reflect how hormones are used in the U.S. at the moment Dr. Colditz said. The trial has however been held up for years as the gold standard for medical research and its findings linking combination hormones to breast cancer and heart problems led to significant changes in the way doctors around the world treated menopause. A major caveat in interpreting the new estrogen data is that the study used conjugated equine estrogens which are estrogen compounds derived from the urine of pregnant mares and marketed by Wyeth Pharmaceuticals under the brand Premarin. The brand has fallen out of favor with many women who are choosing treatments that contain estradiol which is chemically similar to a womans natural estrogen. It is not known whether the benefits of estrogen shown in the Womens Health Initiative would be replicated using a different type of estrogen. Nobody knows why estrogen treatment alone appeared to lower breast cancer risk in the study but one explanation may be that in menopausal women with low levels of natural estrogen the effects of estrogen drugs induce cell death in existing tumors httpshealth.nytimes.comhealthguidesdiseasetumoroverview.htmlinlinenytclassifier. Nobody is suggesting that women start using estrogen to prevent breast cancer but the finding opens a potentially new avenue of research in the prevention of the disease. We need to look closely at these findings to see if we can learn more about ways to prevent breast cancer in women said Dr. JoAnn Manson a Womens Health Initiative investigator and an author of the study who is chief of preventive medicine httpshealth.nytimes.comhealthguidesspecialtopicpreventivehealthcareoverview.htmlinlinenytclassifier at Brigham and Womens Hospital httpstopics.nytimes.comtopreferencetimestopicsorganizationsbbrigham_and_womens_hospitalindex.htmlinlinenytorg in Boston. In the final analysis of the estrogenonly trial use of the hormone was not associated with any significant risks or benefits pertaining to blood clots stroke httpshealth.nytimes.comhealthguidesdiseasestrokeoverview.htmlinlinenytclassifier hip fracture httpshealth.nytimes.comhealthguidesinjurybrokenboneoverview.htmlinlinenytclassifier colon cancer httpshealth.nytimes.comhealthguidesdiseasecoloncanceroverview.htmlinlinenytclassifier or overall death rates. But there were surprising differences in the risks and benefits of estrogen use on heart risk when comparing the youngest and oldest women in the study. Women who were in their s when they first started using estrogen also had significantly fewer heart risks including almost  percent fewer heart attacks compared with those assigned to the placebo group. The data indicate that for every  women in their s those using estrogen would experience  fewer heart attacks  fewer deaths and  fewer adverse events like blood clots or stroke in a given year compared with those taking a placebo. But the risks of estrogen use were pronounced in older women. For every  women in their s using estrogen would cause  extra heart attacks  extra deaths and  serious adverse events. The big message there is that the data look much more favorable for younger women and much riskier for older women said Dr. LaCroix. Dr. Rowan Chlebowski another author of the study and a medical oncologist at Los Angeles Biomedical Research Institute said the findings underscored the fact that the risks and benefits of menopause hormones change depending on a womans health status her age and the type of hormone used. Dr. Chlebowski previously led research that showed cancer httpshealth.nytimes.comhealthguidesdiseasecanceroverview.htmlinlinenytclassifier risks associated with combination hormone therapy but he says the new data on estrogen alone show that in certain women estrogen use to relieve menopausal symptoms is a good choice. When you look at the debate people are saying hormones are good or not good  its been all or nothing. This calls attention to the fact that there are differences Dr. Chlebowski said. I hope that separation will become clearer now."