It has been estimated that about 5 to 10 percent of all female breast cancer cases are hereditary. They occur as the result of an inherited alteration in a gene. This means the individual has inherited an increased likelihood for developing breast cancer. In most families with this inherited alteration in a gene, several individuals will be affected with cancer, often at young ages. Male breast cancer may also be hereditary.
Some women are predisposed to breast cancer because they are born with a mutation in one copy of particular genes known as BRCA1 or BRCA2. These genes have normal functions within cells, perhaps as caretakers that repair DNA when it is damaged. When a person is born with one abnormal copy of either of these genes, the other copy is able to make up for it and the cells function normally. However, if the normal copy is damaged, the cell is predisposed to become cancerous. Because one abnormal copy is present in every cell of the body and only one gene must be damaged, individuals who are born with an abnormal BRCA1 or BRCA2 gene are more likely to develop breast cancer and to do so at an earlier age. It does not matter whether the abnormal copy comes from the person's mother or father. These women may also have an increased risk of developing ovarian cancer.
The majority of all breast cancers are NOT hereditary. Of those that are hereditary, about a third are due to mutations in the BRCA1 gene. About a third of the remaining hereditary breast cancers are due to mutations in the BRCA2 gene. There may be additional, as yet unidentified breast cancer genes, which account for the remaining hereditary breast cancer clusters.
Genetic Counseling
If you've been diagnosed with breast cancer, you may be wondering if you and members of your family should be tested for the genes associated with breast cancer. The two most widely publicized are the BRCA1 and BRCA2 genes.
In most cases, the answer is no. The mutated form of the gene is responsible for only a small percentage of breast cancers.
However, you or your relatives might consider genetic counseling (and perhaps testing) if several members of your family in multiple generations have developed breast cancer or other forms of cancer, if breast cancer occurred at a fairly young age, and if it occurred in both breasts. Also, women who are of Ashkenazi (Eastern and Central European) Jewish ancestry and also have a family history of breast or ovarian cancer should consider counseling.
Genetic counseling usually involves several sessions with a trained counselor. The counselor will explore and chart a woman's family history of disease, discuss her personal risk factors, and make an estimate of her risk for disease. She or he will also determine whether the genes BRCA1 and BRCA2 might be a factor and will talk about the emotional aspects of testing for the genes. For example, would you be comfortable knowing that you had a mutated gene that put you at very high risk of disease? Would you be comfortable entrusting your future to periodic screening examinations, or would you feel like you were living under a dark cloud? Would you consider a prophylactic mastectomy (removing healthy breasts) or oophorectomy (removing health ovaries) to try to prevent cancer? Would the knowledge affect your decisions about childbearing? A counselor can help you to explore these issues and decide whether or not you want to be tested.
Remember, genetic testing cannot predict whether or not you or a family member will develop breast cancer. It can only tell you if it is more likely. Some women who have the mutated gene never develop the disease. In addition, a negative result does not mean a woman is guaranteed good health forever - there may be other genes involved in her family that have not yet been identified by scientists. And, even if a genetic test is negative in a family with a known mutation, a woman is still at the same risk as the general population.
To locate a genetic counselor, ask your doctor for a referral or call 1-800-4-CANCER.
