Journal of the National Cancer Institute Advance Access published online on October 7, 2008
JNCI Journal of the National Cancer Institute, doi:10.1093/jnci/djn329
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Published by Oxford University Press 2008.
BRIEF COMMUNICATION |
Prospective Evaluation of Risk Factors for Male Breast Cancer
Affiliations of authors: Hormonal and Reproductive Epidemiology Branch (LAB, DAR, GLG, JVL) and Nutritional Epidemiology Branch (YP, AS), Knowledge Management, AARP, Washington, DC (ARH)
Correspondence to: Louise A. Brinton, PhD, Hormonal and Reproductive Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute. 6120 Executive Blvd, Suite 550, Rm 5018, Rockville, MD 20852-7234 (e-mail: brinton{at}nih.gov).
Most risk factors for male breast cancer have been derived from retrospective studies that may reflect selective recall. In the prospective National Institutes of Health–AARP Diet and Health Study, we studied 324 920 men, among whom 121 developed breast cancer. Men who reported a first-degree relative with breast cancer had an increased risk of breast cancer (relative risk [RR] = 1.92, 95% confidence interval [CI] = 1.19 to 3.09). Among the medical conditions examined, a new finding emerged regarding increased male breast cancer risk associated with a history of a bone fracture (RR = 2.20, 95% CI = 1.24 to 3.91). Obesity was positively related to risk (RR = 1.79, 95% CI = 1.10 to 2.91, for body mass indices of 
30 vs <25 kg/m2) and physical activity inversely related, even after adjustment for body mass index. Smokers were at somewhat elevated risk, although trends with smoking characteristics were inconsistent. Alcohol consumption was not related to risk. The identified risk factors show some commonalities with female breast cancer and indicate the importance of hormonal mechanisms. Differences in risk factors may reflect unique mechanisms associated with androgens and their ratio to bioavailable estrogens.
| CONTEXT AND CAVEATS Prior knowledge Many risk factors for male breast cancer have been identified in studies that may suffer from the selective recall of participants. Study design Prospective cohort study of more than 300 000 men in the National Institutes of Health–AARP Diet and Health Study, who submitted a completed questionnaire and of whom 121 developed breast cancer. Contribution Having a first-degree relative with breast cancer, having a bone fracture after the age of 45 years, and being obese were associated with an increased risk of male breast cancer. Physical activity, after adjustment for body mass index, was inversely related to risk. Alcohol consumption was not related to risk. Implications Commonalities between risk factors for male and female breast cancer indicate that hormonal mechanisms may be important, whereas differences may reflect unique mechanisms that may be associated with androgens. Because of the small number of patients with male breast cancer in this and other studies, however, risk factors for male breast cancer should be investigated further in pooled analyses across many studies. Limitations This study had relatively few participants who developed male breast cancer, which limited its power to detect rare exposures. The generalizability of the results is unclear because the findings were based on self-reported information and the response rate to the questionnaire was low. From the Editors
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Manuscript received March 11, 2008; revised July 31, 2008; accepted August 14, 2008.
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J Natl Cancer Inst 2008 100: 1417.