Approximately 10% of breast cancer is considered "hereditary." The majority of breast cancers, however, are called "sporadic," meaning we don't know why they happened. Hereditary cancer refers to cancer that is caused by a gene mutation that is present at birth and in all cells of the body. This gene change makes individuals more likely to develop cancer in their lifetime but doesn't mean they will definitely develop the disease. Certain cancers, including those of the breast, ovary and colon, are more likely than others to be hereditary.
Important factors in determining if the breast cancer in a family is hereditary include: the age of onset of breast cancer; the presence of certain other types of cancer in a family; and the number of relatives with cancer and their relationship to you. A genetic counselor will look at your family's medical information (called a pedigree) including the medical information on first-degree relatives (parents, siblings and children), second-degree relatives, (grandparents, aunts and uncles) and third-degree relatives (cousins).
The decision to undergo genetic testing is a very personal one. There is no right or wrong choice; however, genetics is an area of cancer research where knowledge is growing rapidly. It is important to get the most up-to-date information from healthcare providers who are specially trained in cancer genetics when you are making the decision whether to have genetic testing.
The benefits of genetic testing can vary depending on individual circumstances. Knowing your genetic status can be very empowering. Should you test positive for a known mutation, genetic testing can allow you to choose medical options to lower your risk for cancer or detect the disease at an early stage. It may also qualify you to participate in research studies that are looking for better ways to detect cancer early or to prevent cancer. However, not everyone views the knowledge of cancer risk as a benefit. The limitations of the test are complex. Genetic testing impacts both the individual undergoing testing and other members of the family. Some people may find the information and uncertainty associated with risk overwhelming, especially at first. And since the test itself can only identify the two most common genes involved in hereditary breast cancer (BRCA1 and BRCA2), under certain circumstances, a negative test may not rule out hereditary breast cancer in your family. Because not every person who carries a mutation will get cancer, it is very important to remember that genetic testing cannot detect breast cancer nor can it tell you with certainty if you will get breast cancer at some point in your life.
There are several options available for breast cancer risk reduction in high-risk women. Chemoprevention involves taking a medication to lower the risk for cancer. Tamoxifen is a medication that has been approved to lower breast cancer risk in certain high-risk women and appears to lower risk by up to 50%. Other medications are being researched. Surgical removal of healthy breasts and/or ovaries, known as prophylactic surgery, can effectively lower the risk for breast cancer in high-risk women as much as 95%. In addition to risk reduction options, increased surveillance tools such as Magnetic Resonance Imaging (MRI) and ultrasound can be used in conjunction with mammography to assist in detecting breast cancer at its earliest and most treatable stage. These tools and others, such as ductal lavage, are currently being studied to see if they improve outcome for high-risk women who choose surveillance. None of these options eliminate the risk for breast cancer. In addition, each option has its own benefits and risks. It is important to choose a healthcare team that is trained in managing high-risk women and discuss each option thoroughly with them.
BRCA1 and BRCA2 are the two most well-known genetic mutations that can predispose a woman to breast cancer. The BRCA 1 and 2 genes help to suppress tumor growth under normal circumstances. However, an individual with a BRCA1 or BRCA2 gene mutation has a significantly higher risk of developing breast, ovarian or other cancers including melanoma and prostate cancer in men.