Background: Colorectal cancer remains the fourth most common cancer diagnosed and the second most common cause of cancer death in the United States. Though incidence and mortality rates have declined in recent years, the burden of disease is disproportionate; rates are higher in men than women and the male-to-female incidence rate ratio (MF IRR) increases progressively across the colon from the cecum to the rectum. Rates among races/ethnicities other than whites or blacks have not been frequently reported.

Methods: To examine colorectal cancer rates by sex across anatomic subsite, age, and racial/ethnic groups, we used the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) program for cases diagnosed among residents of 13 registries during 1992-2006. Incidence rates were expressed per 100,000 person-years and age-adjusted to the 2000 US Standard Population; male-to-female incidence rate ratios (MF IRR) and 95% confidence intervals were also calculated.

Results: Among both males and females, total colorectal cancer rates were highest among Blacks (71.0 and 54.8 per 100,000 person-years, respectively) and lowest among Hispanics (47.8 and 32.4). Rates of proximal colorectal cancer were higher than distal and rectal sites for all race/ethnicities. Among each racial/ethnic group, the MF IRR increased fairly monotonically from close to unity for cecal cancers to 1.81 (Hispanics) for rectal cancers. MF IRRs increased with age most rapidly for distal colon cancers from <1.0 at ages <50 years to 1.4-1.9 at older ages. The MF IRR for rectal cancers also rose with age from about 1.0 to 2.0. For proximal cancer, the MF IRR was consistently <1.5 and varied little with age; among American Indian/Alaska Natives it was <1.0 across all ages.

Conclusion: The MF IRR for colorectal cancer varies markedly according to subsite and age but less by racial/ethnic group. These findings may reflect differing exposure to, or metabolism of, hormonal or environmental elements and may have consequences for screening messages.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1817.