LAUSR

Male breast cancer (MBC) accounts for 1% of all breast cancer. Adult obesity and tallness are risk factors for MBC, but the role of adolescent fatness is largely unknown. We aimed to assess the association between body mass index (BMI) in adolescence and the incidence of MBC in a large cohort of 16‐ to 19‐year‐old Israeli males. 1,382,093 Jewish Israeli males aged 16–19 who underwent anthropometric measurements, a general intelligence test (GIT) and other examinations during 1967–2011, were followed up to December 31, 2012 for MBC incidence. Cox proportional hazards models assessed the association between adolescent BMI (as WHO BMI categories and as age‐specific CDC percentiles) and time to MBC diagnosis, adjusting for sociodemographic covariates. Of 100 MBC cases diagnosed during 29,386,233 person‐years of follow‐up, 97 were included in multivariable analyses. Compared to “healthy” BMI (18.5–24.9 kg/m2) and adjusted for year of birth, country of origin and GIT score, higher adolescent BMI was associated with higher MBC risk: hazard ratio (HR) = 2.01 (95% confidence interval [CI] 1.14–3.55, p = 0.015) in overweight (25.0 ≤ BMI < 30.0 kg/m2) adolescents; and HR = 4.97 (95%CI 2.14–11.53, p = 0.0002) in obese (BMI ≥ 30.0 kg/m2) adolescents. When CDC age‐specific BMI percentiles were assessed results were similar and statistically significant for obesity. In addition, low (vs. high) GIT score (HR = 4.76, 95%CI 1.96–12.50, p = 0.001) and European (vs. west‐Asian) origin (HR = 1.99, 95%CI 1.19–3.34, p = 0.009) were independent predictors of MBC. Measured adolescent overweight and obesity are associated with increased risk of MBC, suggesting a modifiable risk factor potentially allowing for early intervention. The novel association with cognitive function should be further explored.