Background: Characteristics that determine the anatomic site within the colorectum where carcinoma is most likely to occur would be useful in choosing optimal modalities for cancer screening and in the study of etiology. The aim of this study was to identify any association of gender, race, or age with colorectal carcinoma in the proximal or distal colorectum.
Methods: A descriptive, population-based epidemiologic study was conducted on colorectal carcinoma (CRC) cases identified through the Illinois Tumor Registry. Among CRC patients diagnosed between 1986 and 1991, age at diagnosis (40-90 years), gender, white or African American race, and subsite of CRC location were identified. Incidence rates were determined with demographic data from the 1990 Illinois census. Logistic regression was used to identify significant subsite specific risk factors for CRC.
Results: During the study period, 38,931 cases of CRC occurred in Illinois among whites and African Americans between the ages of 40 and 90 years. Age, race, and gender were independently significantly associated with both proximal and distal CRC risk (P < 0.0001). The greatest risk for white males was for distal CRC, followed by the risk for African American males of developing CRC in the distal colorectum. African Americans were more likely than whites to develop proximal CRC (odds ratio [OR] = 1.19), whereas whites were more likely to have distal CRC than African Americans (OR = 1.26). Regarding the development of CRC anywhere in the colorectum, male incidence rates adjusted for age and race were greater than rates for females (OR = 1.32 for proximal and 1.68 for distal).
Conclusions: The division of the colorectum anatomically in these analyses at the junction of the descending and sigmoid colon, and including the rectum above the anal canal with "distal" CRC, demonstrated a predominance of African Americans among those at risk for proximal colon carcinoma and a predominance of white males among those at risk for distal CRC; these predominances were clearer than in previous reports. These findings may have a role in the selection of optimal CRC screening strategies for each gender or racial group.