Abstract B145: Validation of a colorectal cancer risk prediction model in US Black women

Background: The National Cancer Institute’s Colorectal Cancer Risk Assessment Tool (NCI-CCRAT) estimates an individual's five-year risk of developing colorectal cancer. It was developed by estimating relative risks from a population of US White women and men and incorporating race, gender, and age-specific incidence data from population-based cancer registries. However, the model performance has not been assessed for Black Americans, who have the highest colorectal cancer incidence and mortality rates of any US racial/ethnic group. Methods: The NCI-CCRAT estimates the absolute risk of colorectal cancer based on an individual’s age, sex, family history of colorectal cancer, sigmoidoscopy/colonoscopy, polyps, smoking, physical activity, regular aspirin/nonsteroidal anti-inflammatory drug (NSAID) use, vegetable intake, body mass index, and hormone replacement therapy use. Validation of the NCI-CCRAT was performed using prospective data from 57,558 participants ages 40 to 84 years in the Black Women's Health Study (BWHS). We predicted 5-year absolute risk using data from 2001 through 2015 in three 5-year prediction periods: 2001-2005, 2006-2010, and 2011-2015. To assess model performance, we computed calibration by comparing the expected number of colorectal cancer cases predicted by the model to the observed number of cases (E/O) in the BWHS overall and in subgroups of the population. We assessed discriminatory accuracy by calculating the area under the curve (AUC). Results: During follow-up from 2001 through 2015 (634,512 person-years), 433 BWHS participants developed invasive colorectal cancer. Based on the NCI-CCRAT, 543 cases were expected. The NCI-CCRAT was well-calibrated in the first 5-year prediction period (2001-2005 E/O=1.03, 95% CI: 0.88–1.21), but the model overestimated risk in the subsequent 5-year prediction periods, with E/O=1.30 for 2006-2010 and E/O=1.44 for 2011-2015. The overall E/O ratio was 1.25 (95% confidence interval: 1.14–1.38), indicating that NCI-CCRAT overestimated the number of cases in this population of Black women. Of note, associations with colorectal cancer were weaker in the BWHS than in the development cohort for vigorous physical activity, aspirin/NSAID use, vegetable intake, and body mass index. We estimated discriminatory accuracy only for the first 5-year prediction period (2001-2005, N cases=151) for which the model was well calibrated, and obtained an age-adjusted AUC of 0.61 (95% CI: 0.57–0.66). Conclusions: The NCI