Investigating the association between anthropometry and colorectal cancer survival: a two-sample Mendelian randomization analysis.

[BACKGROUND] Observational epidemiologic studies on the association of anthropometric traits and colorectal cancer (CRC) survival provide inconsistent results, and potential limitations prohibit the investigation of causality. We examined the associations between seven genetically predicted anthropometric traits [height, body mass index (BMI), waist circumference (WC), hip circumference (HC), waist-hip circumference ratio, birth weight and body fat percentage] and CRC-specific mortality among CRC cases using two-sample Mendelian randomization (MR).

[METHODS] Analyses were performed using 16 964 CRC cases, out of which 4010 died due to their disease, from the Genetics and Epidemiology of Colorectal Cancer Consortium and Colon Cancer Family Registry. We further conducted stratified analyses by anatomical site and stage. We applied the inverse variance weighted approach, and sensitivity analyses were conducted to assess the impact of potential violations of MR assumptions and adjust for collider bias.

[RESULTS] One standard deviation (SD 13.4 cm) higher genetically predicted levels of WC were associated with worse CRC survival [hazard ratio (HR); 1.22, 95% confidence interval (CI); 1.02-1.47]. Positive associations were further observed for a SD higher genetically predicted BMI (SD; 4.8 kg/m2, HR; 1.5, 95% CI; 1.15-1.95) and HC (SD; 9.2 cm, HR; 1.32, 95% CI; 1.02-1.73) and CRC-specific mortality in cases of stages II/III. The latter associations were generally robust to sensitivity analyses. Positive but imprecisely estimated associations were found for most other anthropometric traits.

[CONCLUSIONS] Despite the limitations of cancer survival research, our findings support that CRC cases should avoid obesity. Further research should inform the development of recommendations targeting overweight/obesity management during cancer surveillance.