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Body size, sex and sidedness of incident colorectal cancer in a prospective Swedish cohort study

Abstract Background Obesity is a well-known risk factor for colorectal cancer (CRC), the relative risk being higher in men than in women, and for colon than for rectal cancer. Whether this risk differs by sidedness of colon cancer and sex, has however not yet been explored. Methods Among 28098 participants in the Malmo Diet and Cancer study, 11063 men and 17035 women, 584 incident CRC cases had been registered by Dec 31 2008. Seven anthropometric factors; height, weight, bodyfat%, hip circumference, waist circumference, BMI and waist-hip ratio (WHR) were categorized into quartiles (Q). Hazard ratios (HR) of CRC risk according to tumour location (right colon, left colon, rectum) and sex were calculated using multivariable Cox regression models, adjusted for age, smoking, educational level and alcohol intake. Results In men, several anthropometric factors were associated with an increased risk of right-sided colon cancer (HR for Q1[ref]-Q4 for weight 1.0, 1.67, 1.99, 2.88, ptrend= 0.001; waist circumference 1.0, 0.64, 1.59, 2.03, ptrend= 0.002; WHR 1.0, 0.73, 1.93, 1.89, ptrend= 0.004; BMI 1.0, 1.29, 1.50, 2.64, ptrend= 0.001), only WHR with left-sided colon cancer (1.0, 1.26, 1.94, 2.06, ptrend= 0.021), and none with rectal cancer. In women, body size was not associated with risk for neither right-sided nor left-sided colon cancer, only with rectal cancer (bodyfat% 1.0, 1.57, 2.18, 1.94, ptrend= 0.032, hip circumference 1.0, 1.76, 1.45, 2.18, ptrend= 0.033). Significant interactions with sex were denoted for hip circumference (p = 0.032) and BMI (p = 0.026) in relation to risk of right-sided colon cancer. Conclusions These data unveil a sexual dimorphism in the relationship between obesity and right-sided colon cancer, only being evident in men. As right-sided tumours are otherwise more common in women, hormonal factors may be particularly influential in their carcinogenesis. Legal entity responsible for the study Lund University. Funding The Swedish Cancer Society, the Swedish Research Council, the Swedish Government Grant for Clinical Research, the Mrs Berta Kamprad Foundation, Lund University Faculty of Medicine and University Hospital Research Grants. Disclosure All authors have declared no conflicts of interest.