Objective: The objectives of the current study were to examine the trends in incidence rates of subsite-specific colorectal cancer at all stages in a large US population and to explore the impact of age and sex on colorectal cancer incidence.
Methods: Data were obtained from the Surveillance, Epidemiology, and End Results (SEER) 9 registries. Colorectal cancer incidence was divided into 3 anatomic subsite groupings: proximal colon, distal colon, and rectum. Incidence rates and relative risk were calculated using the SEER*Stat software provided by the National Cancer Institute.
Results: From 1976 to 2005, age-adjusted incidence of proximal colon, distal colon, and rectal cancers per 100,000 population have steadily decreased from 22.5, 18.8, and 19.2 to 21.1, 11.7, and 13.6, respectively, contributing to the overall decline in the incidence of colorectal cancer from 60.5 to 46.4. Distal colon cancer had the greatest incidence decline (-37.79%), whereas the most minimal change in the incidence rates occurred for proximal colon cancer (-6.37%) because of increased incidence rates of ascending colon (24.8%) and hepatic flexure (21.3%) over 30 years. The steadily increased proportion of proximal colorectal cancer subsites was observed in both men and women starting at age 50 although women experienced a greater increase than did men.
Conclusions: Overall incidence rate of colorectal cancer decreased over the past 3 decades. The percent of ascending colon and hepatic flexure cancers diagnosed at early stages (localized and regional) increased. The finding on sex difference over years suggests that great attention should be paid in the future studies to male and female disparities.