Breast cancer risk may be increased in women who have first-degree relatives with a history of prostate cancer

Having a family history of prostate cancer among first-degree relatives may increase a woman's risk of developing breast cancer. That is the conclusion of a new study published early online in CANCER, a peer-reviewed journal of the American Cancer Society. The study's results indicate that clinicians should take a complete family history of all cancers - even those in family members of the opposite sex - to help assess a patient's risk of developing cancer.

Evidence suggests that the risk of developing breast and prostate cancer is increased among individuals with a family history of the same disease, particularly among first-degree relatives. However, less is known about the relationship between breast and prostate cancer within families.

To investigate, Jennifer L. Beebe-Dimmer, PhD, MPH, of the Barbara Ann Karmanos Cancer Institute and Wayne State University School of Medicine in Detroit, studied 78,171 women who enrolled in the Women's Health Initiative Observational Study between 1993 and 1998 and were free of breast cancer at the start of the study. During follow-up, which ended in 2009, a total of 3506 breast cancer cases were diagnosed. The researchers found that a family history of prostate cancer in first-degree relatives (fathers, brothers, and sons) was linked with a 14 percent increase in breast cancer risk for women, after adjusting for various patient factors. In separate analyses examining the joint impact of both cancers, a family history of both breast and prostate cancer was linked with a 78 percent increase in breast cancer risk. Risks associated with a family history of both breast and prostate cancer were higher among African American women than white women.

"The increase in breast cancer risk associated with having a positive family history of prostate cancer is modest; however, women with a family history of both breast and prostate cancer among first-degree relatives have an almost 2-fold increase in risk of breast cancer," said Dr. Beebe-Dimmer.

What is the average American woman’s risk of developing breast cancer during her lifetime?

Based on current incidence rates, 12.4 percent of women born in the United States today will develop breast cancer at some time during their lives. This estimate, from the most recent SEER Cancer Statistics Review (a report published annually by the National Cancer Institute’s [NCI] Surveillance, Epidemiology, and End Results [SEER] Program), is based on breast cancer statistics for the years 2007 through 2009.

This estimate means that, if the current incidence rate stays the same, a woman born today has about a 1 in 8 chance of being diagnosed with breast cancer at some time during her life. On the other hand, the chance that she will never have breast cancer is 87.6 percent, or about 7 in 8.

In the 1970s, the lifetime risk of being diagnosed with breast cancer in the United States was just under 10 percent (or about 1 in 10).