Obesity and Breast Cancer Risk in Men: A National Case-Control Study in England and Wales

Abstract

Background Breast cancer is rare in men, and information on its causes is very limited, from studies that have generally been small. Adult obesity has been shown as a risk factor but more detailed anthropometric relations have not been investigated. Methods We conducted an interview population-based case-control study of breast cancer in men in England and Wales including 1,998 cases incident during 2005–2017 at ages under 80 years and 1,597 male controls, with questions asked about a range of anthropometric variables at several ages. All tests of statistical significance were two-sided. Results Risk of breast cancer statistically significantly increased with increasing body mass index (BMI) at ages 20 (odds ratio [OR]=1.07, 95% confidence interval [CI] = 1.02 to 1.12 per 2-unit change in BMI), 40 (OR = 1.11, 95% CI = 1.07 to 1.16), and 60 (OR = 1.14, 95% CI = 1.09 to 1.19) years but there was also an indication of raised risk for the lowest BMIs. Large waist circumference 5 years before interview was more strongly associated than was BMI with risk, and each showed independent associations. Associations were similar for invasive and in situ tumors separately and stronger for human epidermal growth factor receptor 2 (HER2)-positive than HER2-negativetumors. Ninety-nine percent of tumors were estrogen receptor-positive. Conclusions Obesity at all adult ages, particularly recent abdominal obesity, is associated with raised risk of breast cancer in men, probably because of conversion of testosterone to estrogens by aromatase in adipose tissue. The association is particularly strong for HER2-expressingtumors.

Toward Understanding the Etiology of Male Breast Cancer: An Ongoing Research Challenge

“…The pooling project reported a 19% increased risk per 5-unit increase in BMI (OR = 1.19, 95% CI = 1.1 to 1.3) and a 35% statistically significantly increased risk for obese men (BMI ≥ 30 kg/m 2 ) compared with normal weight men (BMI = 18.5-24.9 kg/m 2 ) ( 4 ). Generally consistent with this information, Swerdlow et al ( 10 ) found that recent waist-to-height ratio was a stronger risk factor than that at age 20 years.…”

“…In summary, findings from the study by Swerdlow and colleagues ( 10 ) provide additional evidence of the detrimental role of obesity and central obesity on breast cancer risk and warrant further studies. Ideally, future research efforts examining the association of obesity and male breast cancer should use a prospective design; include a diverse population of men, particularly Black men, and sufficient sample size to classify men according to clinically meaningful BMI categories; evaluate risk by tumor subtypes; and conduct anthropometric measurements to be able to characterize body fat distribution and body composition.…”

“…In this issue of the Journal, Swerdlow and colleagues ( 10 ) present evidence based on 1998 male breast cancer cases and 1597 controls that greater BMI and abdominal obesity are associated with increased risk of breast cancer in men. Considering the sparse evidence highlighted above, these are important and novel findings that leverage data from a large British population-based case-control study over a 12-year period, representing one of the largest and most detailed studies examining this association to date.…”

“…Notably, no previous study has examined the association of central obesity and male breast cancer. Overall, Swerdlow et al ( 10 ) make a unique contribution to the literature with this analysis by examining the associations with BMI and central obesity at different ages.…”

“…It should be noted that, although the study by Swerdlow and colleagues ( 10 ) was one of the largest studies examining these associations to date, their study population was primarily comprised of White men (94% of cases and 98% of controls). As such, these findings may not be generalizable to other racial and ethnic groups, which may have different rates of obesity and other social and environmental factors that may be associated with cancer risk as well as different patterns of breast cancer subtypes.…”