Breast Cancer in the Family

Breast cancer usually occurs without any noticeable family inheritance pattern. However, about 5 percent of breast cancer cases show a "clustering" within a single family. In families where two or more relatives have breast cancer, there are often mutations (alterations) of the genes known as BRCA-1 or BRCA-2. (BRCA-1 stands for the first gene discovered that was associated with BReast CAncer; BRCA-2 is the second gene discovered.) Knowing your genetic risk for breast cancer will help your doctor to map out a strategy for breast cancer surveillance. In addition, your doctor may recommend certain medications or enroll you in a clinical trial.

A single gene mutation does not cause a breast tumor to grow. Any kind of cancer involves a complex interaction of inherited and environmental factors. The following background information is intended to help you appreciate this complexity and guide your further reading.

What is a gene?

Genes are molecules on 46 supporting structures, called chromosomes, located in the nucleus of every cell. Thousands of genes make up our "genome," each of which provides chemical instructions for all the cell's functions, from division, repair to the production of eye color.

How are genes involved with cancer?

Oncogenes are a set of genes that tell a cell to divide, to repair itself or to self-destruct if damage cannot be repaired. Damaged genes, or mutations, fail to give proper instructions, and may not even work at all. Mutations of oncogenes, whether inherited from a parent or caused by radiation, smoking, or some other exposure, lead to cancer.

What do the BRCA genes do?

Research has shown that normal BRCA 1 and 2 are oncogenes with a set of instructions for making proteins that enable a cell to "recognize" damage and to stop dividing. In other words, these genes keep faulty cells from reproducing.

How are the BRCA genes involved with breast cancer?

Mutations of BRCA genes are inherited either from your mother or father. Specific mutations have already been identified; some are believed, in a sense, to make the cell blind to its own damage. A "blind" cell tends to divide, rather than pause and let itself be repaired. Proliferation of damaged cells in breast tissue due to BRCA mutations is one of many steps that must occur over years before a malignant breast tumor forms. BRCA mutations mean only that there is a risk for breast cancer, not that it will definitely develop.

Genetic patterns of breast cancer

• Family clustering.
  • Two sisters OR a mother-daughter pair with breast cancer
  • A single member of two non-consecutive generations (for example, a woman has breast cancer, her daughter does not, but her granddaughter develops the disease).

• Breast cancer in certain populations.
  • BRCA gene mutations are significantly seen in Ashkenazis (people of Central or Eastern European Jewish heritage).
  • Women of Northern European decent (Dutch, Norwegian and Icelandic ancestry) tend to inherit other genetic mutations related to breast cancer.

• Women younger than 45 years.

• Ovarian cancer may also appear in families with the BRCA gene mutations. Some families have a strong history for both breast and ovarian cancer.

How do BRCA genes increase the risk of cancer?

Women who inherit a BRCA mutation have a 50% to 85% chance of developing breast cancer in their lifetime. (Women who have an average risk for breast cancer have about a 12% chance of getting breast cancer in their lifetime.) The risk of ovarian cancer with BRCA mutations increases to about 40%.

Benefits of BRCA testing

• A positive test will prompt your doctor to follow you more closely. For instance, you may have more frequent mammography.
• Testing also helps to identify other family members who may be at risk.

Limits of BRCA test

• A positive test only indicates an increased risk for developing breast cancer. It does not mean someone will definitely develop the disease.
• A negative test result only eliminates the known BRCA mutations associated with breast cancer, and says nothing about other potentially important mutations that research has not discovered.
• Whether the results are positive or negative, the test may not calm anxieties about breast cancer risk.

What you can do

Talk to your doctor after answering these questions:

• Who in your family has breast cancer?
• How old were they when they found out they had breast cancer?
• Which grandmother(s) had breast cancer? Find out about your father's mother as well as your maternal grandmother.
• Are there other types of cancer in the family?

Learn about genetic testing for breast cancer. Your doctor may suggest that you speak to a genetic counselor and go for genetic testing. A genetic counselor is trained to look very closely into your family history and identify what types of testing will benefit you the most. Remember: if you are offered BRCA gene testing, the results only identify your risk for breast cancer. Genetic counseling is vital.

Learn about experimental treatments for BRCA positive women or those with a strong breast cancer family history. Your doctor may want to enroll you in a clinical trial that uses estrogen receptor blockers, tamoxifen and raloxifene. These have helped to prevent recurrence in women already treated for breast cancer.

Related Articles Should You Have a Mastectomy to Prevent Breast Cancer? Compiling a Family Health History

External Sources "Learning About Breast Cancer" National Human Genome Research Institute Genetics Home Reference Your Guide to Understanding Genetic Conditions Fact Sheet on Genetic Testing for Breast and Ovarian Cancer Susceptibility

This article was reviewed and updated June 2007.

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