What Makes a Woman Likely to Get Breast Cancer?

There's no way yet to predict who is most likely to get breast cancer. Although a few men get the disease, the overwhelming majority of people with breast cancer are women. Research shows some women have a higher chance of getting the disease than others. Before age 45, African American women have the highest chance of getting breast cancer, compared to women from other ethnic groups. After age 45, white women are most likely to get the disease.

Here's a summary of characteristics that can lower or raise a woman's chances of getting breast cancer. Each characteristic by itself has only a small effect on risk.

These Characteristics Raise a Woman's
Chances of Getting Breast Cancer

These Characteristics Lower a Woman's
Chances of Getting Breast Cancer

Older Age Younger Age
White Asian/Pacific Islander
African American Hispanic
Jewish No corresponding factor
Never married Married
Higher income and more education Lower income and less education
Immigrated from a low-income nation to a highincome nation No corresponding factor
Never had a baby No corresponding factor
Had first baby after age 30 Had first baby after age 20
Began menstruating before age 12 Began menstruating after age 12
Reached menopause after age 55 Reached menopause before age 55
Taking or recently took estrogen replacement therapy (especially for many years with high-dose combined estrogen and progestin) No corresponding factor
Taking birth control pills or took them less than 10 years ago No corresponding factor
Taller Shorter
After menopause, higher weight relative to height Before menopause, higher weight relative to height
Drinking two or more alcoholic drinks per day Regular exercise as an adult
No corresponding factor Exercise as a teenager reduces the chance of getting breast cancer before menopause
Exposure to radiation (at higher levels than from mammograms) No corresponding factor
Inheriting breast cancer susceptibility genes No corresponding factor
A sister, mother, or both who had breast cancer No corresponding factor
Already had breast cancer No corresponding factor
Had benign breast disease, especially atypical hyperplasia No corresponding factor
On a mammogram, breasts look very dense No corresponding factor

In about half of all breast cancer cases, none of the characteristics listed on the previous page make any difference. Inherited genes, for example, play a role in only 5 to 10 percent of breast cancer cases. In addition, most of the characteristics listed above are probably not direct causes. We don't know why they affect a woman's risk for breast cancer. What makes a particular woman get breast cancer is still a puzzle that can only be solved with more research.

How This Research Was Done

Researchers summarized results from many scientific studies published in respected journals over the past decade. The studies summarized here were for the most part based on samples of women from the U.S. population, and they did not necessarily include women from California. Information in this section comes from Chapter 2 of Breast Cancer in California, 2003, “Risk Factors for Female Breast Cancer,” by Rosemary D. Cress, Dr.P.H.