Geographic variation in the incidence of colorectal cancer in the United States, 1998-2001

BACKGROUND. This study examined the incidence rates and risk factors for colorectal cancer in 9 geographic divisions in the United States. METHODS. The colorectal cancer cases were diagnosed between 1998 and 2001 in 39 states and the District of Columbia (grouped into 9 geographic divisions in the United States). The association between colorectal cancer and geographic division was analyzed using the Poisson regression model controlling for demographics and ecologic measures of education, behavioral factors and colorectal cancer screening data extracted from the Behavioral Risk Factor Surveillance System. RESULTS. The age-adjusted incidence rates of colorectal cancer were highest in the Middle Atlantic division, followed by New England division, East and West North Central divisions, East South Central and South Atlantic divisions, West South Central and Pacific divisions, with the lowest rate observed in the Mountain division. Old age, male gender, black race, less than a twelfth-grade education, smoking, and no physical activity were significantly associated with higher incidence rates of colorectal cancer, whereas having sigmoidoscopy/colonoscopy in the past 5 years, fecal occult blood test in the past year, and obesity were associated with lower incidence rates of colorectal cancer. The relative ranking of incidence rates of colorectal cancer across divisions changed after adjusting for these factors. CONCLUSIONS. Significant geographic variation in colorectal cancer exists in the United States. Risk factors, including demographics, education, behavior, and screening use, can only partially explain the differences across geographic divisions.