Racial/ethnic differences in colorectal cancer risk: the multiethnic cohort study

Incidence rates in the United States show clear racial/ethnic disparities for colorectal cancer. We examined the extent to which ethnic differences in risk factors could explain the age-adjusted variation in the risk of colorectal cancer, overall and by stage at diagnosis, among 165,711 African Americans, Japanese Americans, Latinos, Native Hawaiians and whites participating in the Multiethnic Cohort Study. Over a median follow-up period of 10.7 years, 2,564 incident cases of colorectal cancer were identified through surveillance, epidemiology and end result tumor registry linkages in Hawaii and California. Multivariable-adjusted Cox proportional hazard models were used to estimate relative risks (RR) and 95% confidence intervals (CI) for each ethnic group compared to whites. After accounting for known/suspected risk factors, Japanese Americans (men, RR = 1.27, 95% CI = 1.09-1.48; women, RR = 1.49, 95% CI = 1.24-1.78) and African American women (RR = 1.48, 95% CI = 1.23-1.79) remained at increased risk of colorectal cancer relative to whites; African American and Japanese American women were also at increased risk of advanced disease compared to whites. In site-specific analyses, after multivariable adjustment, African Americans (both sexes) and Japanese American women remained at increased risk for colon cancer, and Japanese Americans (both sexes) and Native Hawaiian men for rectal cancer compared to whites. The results of our study suggest that differences in the distribution of known/suspected risk factors account for only a modest proportion of the ethnic variation in colorectal cancer risk and that other factors, possibly including genetic susceptibility, are important contributors to the observed disparities in incidence.