A significant number of women with breast cancer have a family history of the disease, but only 5 to 10 percent of all breast cancer cases are actually hereditary. A woman is two to three times more likely than the general population to develop breast cancer if a first-degree relative (mother, sister, or daughter) has had the disease. If more than one close relative has had breast cancer, the risk is higher.
This increased risk is even higher if the relatives developed cancer either before the onset of menopause or in both breasts. In addition, the presence of other certain types of cancer, such as ovarian cancer and male breast cancer, increase the possibility that the cancer is hereditary.
BRCA Gene Mutations
Some patients with family histories of breast cancer are predisposed to the disease because they are born with mutations in the BRCA1 or BRCA2 genes. A woman can inherit an abnormal (mutated) BRCA1 or BRCA2 gene — or rarely, both — from either her father or her mother. These genes normally function as “caretakers” to repair DNA in cells when the DNA becomes damaged. Women without the BRCA mutation who have two normal copies of the gene are at lower risk for developing cancer. However, when a person is born with one abnormal copy of either of these genes, she is at higher risk of developing breast cancer.
Genetic counselors at Memorial Sloan-Kettering help patients to understand the implications of genetic testing for cancer risk.
In addition to breast cancer, women with BRCA mutations have an increased risk of developing ovarian cancer, and males with these mutations may be at increased risk of developing male breast cancer and prostate cancer. The chance that a woman with breast cancer has a BRCA mutation is higher if her family history includes people with these kinds of cancer (especially ovarian and male breast cancers).
In addition to BRCA1 and BRCA2, there are other genes involved in the development of breast cancer. Research is under way to find such genes and their modifiers.
If you have been diagnosed with breast cancer, you may wonder if you and members of your family should be tested for the gene mutations associated with breast cancer. In most cases, the answer is no. Inherited gene mutations are responsible for only a small percentage of breast cancers.
However, you and your relatives might consider genetic counseling (and perhaps testing) if several members of your family in multiple generations had breast cancer or other forms of cancer (especially ovarian cancer or male breast cancer), if breast cancer occurred at a fairly young age, or if it occurred in both breasts. BRCA mutations are more common in women of Ashkenazi (Eastern and Central European) Jewish ancestry.
Genetic counseling usually involves several sessions with a trained counselor and a blood test. The counselor will explore and chart your family history of disease, discuss your personal risk factors, and estimate your 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 mutations in these genes.
Genetic testing cannot predict whether or not you or a family member will develop breast cancer. It can only tell if it is more likely.
The Clinical Genetics Service at Memorial Sloan-Kettering Cancer Center offers hereditary cancer risk assessment, genetic counseling, and genetic testing by specially trained genetic counselors and physicians for people who are concerned about their personal and/or family history of cancer.