A Comprehensive Model of Colorectal Cancer by Risk Factor Status and Subsite Using Data from the Nurses' Health Study

We expanded and updated our colon cancer risk model to evaluate colorectal cancer (CRC) and whether subsite-specific risk models are warranted. Using data from 1980-2010 for 90,286 women enrolled in the Nurses' Health Study, we performed competing-risks regression and tests for subsite heterogeneity (proximal colon: N = 821; distal colon: N = 521; rectum: N = 376). Risk factors for CRC were consistent with those in our colon cancer model. Processed meat consumption was associated with a higher risk of distal (hazard ratio (HR) = 1.45; P = 0.02) but not proximal (HR = 0.95; P = 0.72) colon cancer. Smoking was associated with both colon (HR = 1.21) and rectal (HR = 1.27) cancer and was more strongly associated with proximal (HR = 1.31) than with distal (HR = 1.04) colon cancer (P = 0.029). We observed a significant trend of cancer risk for smoking in subsites from the cecum (HR = 1.41) to the proximal colon (excluding the cecum; HR = 1.27) to the distal colon (HR = 1.04; P for trend = 0.040). The C statistics for colorectal (C = 0.607), colon (C = 0.603), and rectal (C = 0.639) cancer were similar, although C was slightly higher for rectal cancer. Despite evidence for sitespecific differences for several risk factors, overall our findings support the application of risk prediction models for colon cancer to CRC.