When a woman is diagnosed with breast cancer, the first thing a doctor wants to do is whether she inherited the disease, i.e., is her cancer caused by an abnormal gene inherited from her family? Asking for a detailed family history is the first step, and the clues associated with hereditary breast cancer are as follows: A family history of breast cancer on the mother’s or father’s side. Multiple women on either side are breast cancer. Age less than 50 years at diagnosis Family history of ovarian cancer in the father’s or mother’s family Male breast cancer in the father’s or mother’s family Non-inherited breast cancer Just because there are one or two breast cancer patients in the family does not mean that the woman’s breast cancer is necessarily caused by an inherited abnormal gene in the family. The vast majority of women with a family history of breast cancer do not have the disease caused by an inherited gene, but by an increase in other risk factors. Breast cancer may occur more commonly in a family because of similarities in reproductive and environmental factors, and women in these families have a much lower risk of developing breast cancer than those with genetic mutations. If a woman has a mother or a sister with breast cancer and no other relatives have breast cancer and no genetic abnormalities are found, her risk of getting breast cancer by age 70 is 7 to 18 percent, which increases with the number of relatives with the disease, but is still lower than for women with a definite genetic mutation. Hereditary breast cancer About 5-10% of all breast cancers are hereditary breast cancers. By hereditary, we mean caused by a mutated gene, and several such genes (tumor susceptibility genes) have been identified. BRCA1 and BRCA2 are the first breast cancer genes identified, and 45% of hereditary breast cancers are caused by these two genes, accounting for about 1.5% to 3% of all breast cancers. BRCA1, a gene located on chromosome 17, is found in 30% of people with multiple breast cancers in their family, and up to 90% of families with dual primary ovarian and breast cancers have a BRCA1 mutation. BRCA1 mutations may also be associated with bowel and prostate cancers. BRCA2 mutations may be associated with an increased risk of several cancers, such as bowel cancer, prostate cancer, gallbladder cancer, stomach cancer and melanoma. BRCA2 mutations are associated with breast cancer in men. BRCA1 and BRCA2 are human tumor suppressor genes that normally inhibit tumor growth and their protein products help to detect and repair damaged DAN, once mutated, the repair function is lost and the gene defects accumulate eventually leading to tumorigenesis. BRCA1 and BRCA2 are two very large genes and encode very large molecular amounts of proteins. 2000 different mutations have been identified in BRCA1 and BRCA2, for example in the descendants of Ashkenazi Jews, only two codons are missing in 6000 DNA sequences, and it is this small deletion that increases their susceptibility to breast cancer, and they can produce protein deletions or encode non-functional proteins thereby increasing the risk of breast cancer.