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NCI News Note

NIH study confirms risk factors for male breast cancer

  • Posted: February 19, 2014

One of the largest studies conducted to date pooled data from studies of about 2,400 men with breast cancer and 52,000 men without breast cancer and confirmed that risk factors for male breast cancer include obesity, a rare genetic condition called Klinefelter syndrome, and gynecomastia (excess breast tissue). Male breast cancer is rare, with only about 2,000 new cases expected to be diagnosed in 2014 in the United States. Since men are diagnosed with breast cancer at less than one percent the rate of women, studies on risk factors associated with this cancer in men have been limited in size and scope. Scientists at NCI addressed this issue by pooling risk factor data from over 21 studies on male breast cancer. The results of their work appeared Feb. 19, 2014, in the Journal of National Cancer Institute. 

The scientists, led by Louise Brinton, Ph.D., and Michael B. Cook, Ph.D., NCI, observed a small but statistically significantly elevated risk for breast cancer in men with a high body mass index (BMI). Men with the highest BMI had a 35 percent greater risk of breast cancer compared to men with the lowest BMI. The elevated risk observed with men who have a high BMI (who often have excess breast tissue and elevated estrogen levels) appears similar to the pattern for breast cancer risk in postmenopausal women. It was also determined that gynecomastia, independent from both Klinefelter syndrome and obesity, was associated with a 10-fold increased risk of breast cancer in men. As a next step, Brinton plans to follow up these findings with a deeper analysis of the effects of naturally occurring hormones on the risk of breast cancer in men by testing hormone levels in biological samples available from some of the studies involved with the project.