Circulating levels of testosterone, sex hormone binding globulin and colorectal cancer risk: observational and Mendelian randomization analyses.

Background Epidemiological studies evaluating associations between sex steroid hormones and colorectal cancer risk have yielded inconsistent results. To elucidate the role of circulating levels of testosterone, and sex hormone-binding globulin (SHBG) in colorectal cancer risk we conducted observational and Mendelian randomization (MR) analyses. Methods The observational analyses included 333,530 participants enrolled in the UK Biobank with testosterone and SHBG measured. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using multivariable Cox proportional hazards models. For MR analyses, genetic variants robustly associated with hormone levels were identified and their association with colorectal cancer (42,866 cases/ 42,752 controls) was examined using two-sample MR. Results In the observational analysis, there was little evidence that circulating levels of total testosterone were associated with colorectal cancer risk; the MR analyses showed a greater risk for women (odds ratio per 1-standard deviation (SD): 1.09, 95% CI: 1.01-1.17), although pleiotropy may have biased this result. Higher SHBG concentrations were associated with greater colorectal cancer risk for women (HR per 1-SD: 1.16, 95% CI: 1.05-1.29), but was unsupported by the MR analysis. There was little evidence of associations between free testosterone and colorectal cancer in observational and MR analyses. Conclusions Circulating concentrations of sex hormones are unlikely to be causally associated with colorectal cancer. Additional experimental studies are required to better understand the possible role of androgens in colorectal cancer development. Impact: Our results from large-scale analyses provide little evidence for sex hormone pathways playing a causal role in colorectal cancer development.