One in eight American women will have breast cancer during the course of her lifetime. For most of these women, the cause is not known. Only 5-10% of all breast cancers are related to the presence of a certain inherited mutations in the BRCA1 or BRCA2 (BRCA1/2) genes. Between 20-25% of breast cancers appear in women with strong family history of breast cancer—and no identified BRCA1/2 mutation. 

Everyone has these two genes and mutations occur in all of our genes. But these two mutations represent a disease-causing variance. They cause the gene not to work properly—and its job is to produce a protein that helps the body suppress cancerous changes in cells. However, mutations in BRCA1/2 are not the whole story.

If you have the BRCA1/2 mutations, you have inherited a higher risk for breast cancer—instead of one in eight, your risk is two in three—but breast cancer for you is not a certainty. Researchers know that there are likely other factors, including environmental exposure, hormonal history, gene mutations and gene-to-gene interactions that trigger breast cancer. And, you can have a family history of breast cancer—without those two mutations. Recently, researchers have begun to identify other gene mutations they believe could also be related to breast cancer development.

If you have no family history of breast cancer and no breast cancer-related gene mutation, a mammogram (or 3D mammogram, if available) is a good idea to begin at age 40.

Women with mutations in BRCA1/2 and other risk-associated genes are recommended to begin mammograms at age 25, augmented by an annual MRI, to begin at age 25 in high-risk women.

Women with a strong family history of breast or ovarian cancer should begin mammography and MRI screening at age 30. Many studies have shown that in a high-risk woman, MRI in addition to mammogram can help to find even smaller cancers than mammogram alone.

The alternative for a woman at high risk for breast cancer who does not prefer to do screening would be to consider a preventive surgery to remove her breasts. There is no doubt that preventive mastectomy is the most effective way we know to keep a high-risk woman from ever developing breast cancer. It reduces her chances by 90-95%. 

Yes, especially if you have younger sisters, daughters or nieces. It may not seem like a good thing, but detecting a BRCA1/2 mutation allows other women in the family to be tested and to get a clear, yes-or-no answer about their risks of developing breast and/or ovarian cancer.

Men in the family should also be tested: these gene mutations confer a higher risk of prostate cancer and male breast cancer, and men may have daughters who will be at risk for inheriting the BRCA1/2 mutation. 

Knowing your family history is essential—and not just your mother’s family history, but also your father’s family history. Most people don’t know that genetic mutations can be inherited equally from both sides of your family. Discuss the topic with your family doctor or with a genetic counselor. 

Research in this field is making rapid advances, so what’s known now is less than what will be known in a year or two. For patients who may have considered undergoing genetic testing, or who may have undergone genetic testing and not gotten a solid an answer, a new test is worth considering.

Stanford Health Care's breast cancer genetics experts are now revisiting the charts of patients tested years ago. New genetic tests may find different answers. The understanding of breast cancer genetics is continuously expanding.

You should be tested if:

• You have developed breast cancer at or before age 45
• You have cancer in both breasts or multiple different tumors in one breast
• You have ovarian cancer, at any age and regardless of your family history
• You have another family member who has tested positive for a BRCA1 or BRCA2 mutation
• You have cases of male breast cancer in your family
• You are of Ashkenazi Jewish descent