An increase in body mass index (BMI) or a growing waist size relative to height are significant risk factors for breast cancer in men, independent of obesity per se, according to study results published in Cancer Epidemiology.
Breast cancer is rare in men, and its causes and risk factors are poorly understood. While obesity is a known risk factor, it is not yet known whether weight change is linked to breast cancer risk for men, as it is for women.
Anthony Swerdlow, MD, of the Institute of Cancer Research in London, and colleagues sought to determine if changes in weight and waist size may contribute to increased risk of breast cancer in men.
For the study, 1,998 men diagnosed with breast cancer in England and Wales during 2005 to 2017 and 1,597 men without breast cancer were interviewed about their risk factors including weight and body size at several ages.
The researchers found that breast cancer risk significantly increased with every 2 kilogram per meter squared rise in BMI from the age of 20 to 40 years and from 40 to 60 years. Those who reported a greater increase in adiposity compared with their peers at age 11 were also at higher risk. Further, the risk also rose for those who had an increased waist-to-height ratio from age 20 until five years before breast cancer diagnosis.
The associations between breast cancer risk and increased BMI and higher waist-to-height ratio were independent of each other, and also independent of obesity itself. These links were seen for both in situ (noninvasive) and invasive breast cancer.
“Increases in BMI and abdominal obesity are each risk factors for breast cancer in men, independently of obesity per se,” wrote the researchers. “These associations might relate to increasing estrogen levels with weight gain, but this needs investigation.”