NEW YORK (Reuters Health) – In men, the risk of developing breast cancer is increased by having a first-degree relative with breast cancer, being obese and physically inactive, and “somewhat surprisingly,” having a bone fracture after the age of 45, researchers report in the October 7th issue of the Journal of the National Cancer Institute.

Risk factors for male breast cancer have been largely derived from retrospective studies, which may be affected by participants’ limited recall, Dr. Louise Brinton of the National Cancer Institute in Rockville, Maryland and colleagues note in their report.

They analyzed risk factors for male breast cancer among 324,920 men enrolled in the prospective National Institutes of Health-AARP Diet and Health Study. A total of 121 men developed breast cancer during the study.

According to the researchers, men with either a male or female first-degree relative with breast cancer had nearly a twofold increased risk of breast cancer (relative risk, 1.92), compared with men without an affected relative. The risk was particularly elevated among men with an affected sister (RR = 2.25) and among those with both an affected mother and sister (RR = 9.73).

Unexpectedly, note the researchers, results showed a greater than twofold increased risk of breast cancer in men with a bone fracture occurring after age 45 (RR = 2.20). Such an association has not been seen previously, Dr. Brinton and colleagues say, and was “unexpected because breast cancers are less likely to occur among women with fractures.”

An increased risk of male breast cancer was also associated with obesity (RR = 1.79), and with physical inactivity even after accounting for body mass index.

“The identified risk factors show some commonalities with female breast cancer and indicate the importance of hormonal mechanisms,” Dr. Brinton and colleagues point out. “Differences in risk factors may reflect unique mechanisms associated with androgens and their ratio to bioavailable estrogens,” they conclude.

Reference:
J Natl Cancer Inst 2008;100.