Introduction Colorectal cancer (CRC) affects 150,000 Americans each year and is a major cause of mortality and morbidity. Previous studies have shown that gender is an important factor affecting the incidence of CRC. The purpose of this study was to examine the influence of gender and age on colonic distribution and incidence of CRC in the U.S.
Methods Using the Surveillance, Epidemiology, and End Results (SEER) program of the National Cancer Institute, we identified primary CRC diagnosed between 1973 and 2001. We evaluated temporal changes and analyzed incidence rates per 100,000 person-years based on site, sex and age using the SEER* Stat 5.2 program. Proximal colon is defined as proximal to and including the splenic flexure and distal colon is defined as distal to the splenic flexure including rectum.
Results We identified 366,210 cases of CRC diagnosed from 1973 to 2001, 50 % of which were in males. The CRC incidence increased in both males and females between 1973 and 1985 and decreased thereafter. Throughout the 29-year study period, males consistently had about a 35% higher incidence of CRC than women. When examined by colonic subsite, males also had a higher incidence of CRC than females at all colonic subsites. Throughout the study period, females had a significantly higher proportion of proximal CRC than males (42% vs. 35%). The proportion of proximal CRC steadily increased in both sexes between 1973 and 2001; however this increase was most significant in females. In 1973, proximal CRC was 2/3 as likely as distal CRC in females, but by 2001 distal and proximal CRC rates were equal. In comparison, 2/3 of CRC in males was in the distal colon and only 1/3 in the proximal colon in 2001. Age was also an important factor affecting both the incidence rates and regional distribution of CRC in both sexes. The incidence of CRC in both sexes increased significantly with each successive decade of life. Moreover, there was an age-dependent increase in the proportion of proximal CRC.
Conclusion During the 29-year study period 1973-2001, males had a significantly higher incidence of CRC than females. The CRC incidence increased in both sexes between 1973-1985, then decreased between 1985-2001. Females had significantly higher proportion of CRC in the proximal colon and the proportion of proximal CRC increased during the study period. Age was also an important factor affecting the incidence and distribution of CRC.