Multiple colon polyps within the colon of an individual with familial adenomatous polyposis Although there are over 50 identifiable hereditary forms of cancer, less than 0.3% of the population are carriers of a cancer-related genetic mutation and these make up less than 3–10% of all cancer cases. The vast majority of cancers are non-hereditary ("sporadic cancers"). Hereditary cancers are primarily caused by an inherited genetic defect. A cancer syndrome or family cancer syndrome is a genetic disorder in which inherited genetic mutations in one or more genes predisposes the affected individuals to the development of cancers and may also cause the early onset of these cancers. Although cancer syndromes exhibit an increased risk of cancer, the risk varies. For some of these diseases, cancer is not the primary feature and is a rare consequence. Many of the cancer syndrome cases are caused by mutations in tumor suppressor genes that regulate cell growth. Other common mutations alter the function of DNA repair genes, oncogenes and genes involved in the production of blood vessels. Certain inherited mutations in the genes BRCA1 and BRCA2 with a more than 75% risk of breast cancer and ovarian cancer. Some of the inherited genetic disorders that can cause colorectal cancer include familial adenomatous polyposis and hereditary non-polyposis colon cancer; however, these represent less than 5% of colon cancer cases. In many cases, genetic testing can be used to identify mutated genes or chromosomes that are passed through generations. Gene mutations are classified as germline or somatic depending on the cell type where they appear (germline cells include the egg and the sperm and somatic cells are those forming the body). The germline mutations are carried through generations and increase the risk of cancer. Cancer syndromes * Ataxia telangiectasia * Bloom syndrome * BRCA1 & BRCA2 * Fanconi anemia * Familial adenomatous polyposis * Hereditary breast and ovarian cancer * Hereditary non-polyposis colon cancer * Li-Fraumeni syndrome * Nevoid basal cell carcinoma syndrome * Von Hippel-Lindau disease * Werner syndrome * Xeroderma pigmentosum
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Infectious causes of cancer
Cancer