Last updated: Feb 29, 2016

No one knows very much about why breast cancer happens, except that it likely starts in our genes. "Cancer in general is a disease of aging, and breast cancer is probably caused by an error in gene replication—the older we get, the more error prone we get," says Ramona F. Swaby, MD, a medical oncologist specializing in breast cancer at Fox Chase Cancer Center in Philadelphia. Indeed, a womans chance of getting breast cancer doesnt rise to the terrifying one in eight until shes reached 85 years of age. If youre a woman under 40, for instance, your risk is much lower: one in 233.

Approximatly 5% to 10% of the roughly 200,000 American women diagnosed with breast cancer each year have an inherited gene mutation that puts them at higher risk for developing the disease. Most of these genes remain unidentified, but scientists know that mutations to the BRCA-1 and BRCA-2 (Breast Cancer 1 and 2) genes, which normally help prevent cancer by regulating cell growth, are linked to an increased risk for breast and ovarian cancer.

If youre wondering whether you carry the BRCA-1 or BRCA-2 mutations, you may have considered getting a genetic test to find out. Thats a tough decision, because its not always clear what to do with your test results. Some women who know they are at higher risk without taking the test simply commit to more frequent mammograms; others feel the need to know as much as possible and may consider prophylactic surgery if they test positive.