A small percentage (7-10%) of breast and ovarian cancers are hereditary. A hereditary cancer syndrome refers to a cluster of specific cancers that occur more often in affected families. The characteristics of a hereditary cancer syndrome include: individuals in three or more generations affected with cancer, early age of onset of cancer, bilateral cancer, multiple cancers in one individual and multiple cancers in a family.

Recently, two genes have been discovered, BRCA1 and BRCA2, that have been associated with hereditary breast and ovarian cancer syndromes. BRCA1 and BRCA2 are called tumor suppressor genes. This means that the function of these two genes is to play a role in controlling the rate at which a cell grows and divides. If a cell loses the function of one of these two genes, then it will no longer have the control mechanism in place to regulate cell division, and therefore that cell would grow out of control, thus forming a tumor.

Every person has two copies of each gene, including BRCA1 and BRCA2. Originally, when we were conceived, we inherited one copy of each gene from our mother in the egg cell and one copy from our father in the sperm cell. It is only when both copies of a gene like BRCA1 or BRCA2 become "damaged" or altered that the process of cancer begins. Most of the time we acquire these alterations by chance as part of the normal aging process. However, some individuals are born with one copy of the BRCA1 or BRCA2 gene already altered. These individuals are more susceptible to cancer, and at an earlier age, than are individuals born with two normal working copies of the genes. This is because they only need to acquire one additional alteration to begin the process of cancer.

Alterations in both, BRCA1 and BRCA2 are associated with a significantly increased cancer risk. A woman found to have an alteration in the BRCA1 gene has a lifetime risk to develop breast cancer of 80-85%, a lifetime risk of ovarian cancer of 20-40%, and a small increase in the risk for colon cancer (from 6% to 10%). Men found to have an alteration in BRCA1 also have a small increase in risk for colon and prostate cancers.

Alterations in the BRCA2 gene are also associated with an increased lifetime risk of breast cancer of 80-85%, an increased risk of ovarian cancer of 10-20% (less than with BRCA1), and a small increased risk of several other cancers, possibly including melanoma and pancreatic cancer. Men with BRCA2 mutations are also at increased risk for breast cancer, a relatively rare cancer in men. The risk for male breast cancer is approximately 6% in men found to have an alteration in BRCA2.

BRCA1 and BRCA2 are inherited in a dominant pattern. This means that alterations are passed directly from generation to generation, from parent to child. It does not matter if the person is male or female. A person who inherits a single altered copy of BRCA1 or BRCA2 from his or her parent would be at increased risk to develop cancer. That person is also at risk for passing the gene on to their children. With each pregnancy, the chance of passing the altered gene on to a child is 50/50 or 50%. This means that there is also a 50% chance that the parent passed on the other copy of the gene, the one that was not altered, to the child. That child would not be at increased risk for cancer, and could not pass the alteration on to their children.

In the Ashkenazi Jewish population, three specific mutations (2 in the BRCA1 gene and 1 in the BRCA2 gene) are found to occur more often. The overall frequency of one of these three mutations is approximately 1 in 40 or 2.5% of the Ashkenazi Jewish population. The BRCA1 gene is located on chromosome #17 and the BRCA2 gene is located on chromosome #13.

It is important to understand that both breast and ovarian cancers can be associated with other, less common, hereditary cancer syndromes. If you are concerned about your risk, it is important that you discuss your family history with a genetic counselor to ensure that you have weighed the pros and cons of hereditary cancer syndrome testing, and to ensure that you are pursuing testing for the right hereditary cancer syndrome. If you need help finding a genetic counselor in your area, go to www.nsgc.org.