National Breast Cancer Coalition

Myth #8: Most women with breast cancer have a family history of the disease

FALSE. More than 75% of women with breast cancer have no family history of the disease and less than 10% have a known gene mutation that increases risk.

If you have relatives who have had breast cancer, you may worry that you're next. Family history of breast cancer usually refers to having two or more first-degree relatives (such as a mother, sister, or daughter) or second-degree relatives (such as an aunt, niece or grandmother) who have had breast cancer. The risk for developing breast cancer does increase with increasing numbers of affected first-degree relatives compared with women who have no affected relatives. So, while it is true that women with a family history of breast cancer have an increased risk of developing the disease, most of these women will never get breast cancer.

We have discovered that, among some women with a significant family history, certain inherited mutations of the genes BRCA 1 and BRCA 2 may result in increased risk of breast cancer. The mutations are sometimes (but not always) passed down to relatives. Even if you have a family history, it does not mean you have an inherited mutation. 

BRCA 1 and BRCA 2 mutations are found in about 5-10 percent of all breast cancer cases. Having the mutation does not mean you will automatically get breast cancer; it means you are at higher risk. And remember that 90-95 percent of breast cancer cases do not involve these inherited mutations.

A family history is one risk factor. But a risk factor doesn't cause cancer, it just affects your chance of getting cancer. Other risk factors for breast cancer include getting older, benign breast problems, early exposure to ionizing radiation, having children late in life or not at all, longer exposure to estrogen and progesterone, lack of exercise, and drinking alcohol.  

We know a little about breast cancer risk factors, but why some women develop breast cancer and others do not, is still often a mystery.