Background: Socioeconomic correlates of cancer of the large bowel differ in various countries and calendar periods and may differ for the colon and rectum. Thus, the relationship between education and social class and risk of cancers of the colon and rectum was considered.
Methods: Combination of two hospital-based case-control studies conducted in six Italian centres between 1985 and 1996. Cases were 3533 patients aged < 79, with histologically confirmed cancer of the colon (n = 2180) or rectum (n = 1353), and controls were 7062 patients admitted to hospital for a wide spectrum of acute, non-neoplastic, non-digestive tract diseases.
Results: Compared to individuals with < 7 years of education the multivariate odds ratios (OR) of colon cancer for those with > or = 16 years were 2.45 (95% confidence interval [CI]: 1.87-3.23) in men and 1.29 (95% CI: 0.88-1.90) in women, with significant trends in risk. No significant association emerged between education and risk of rectal cancer, with OR of 1.18 (95% CI: 0.83-1.70) and 1.01 (95% CI: 0.61-1.67) respectively for men and women in the highest educational category compared to the lowest. Social class was also related to colon cancer risk: the OR were 2.30 (95% CI: 1.82-2.90) in men and 1.33 (95% CI: 1.03-1.73) in women in the highest versus the lowest social class. No association was found between social class and rectal cancer risk, with OR of 1.18 for either men or women in the highest as compared to the lowest social class. No significant heterogeneity was found for the association between education and colon cancer risk in either sex across strata of age at diagnosis, coffee, alcohol and vegetable intake, family history of the disease, and in anatomical subsites within the colon.
Conclusion: This study, based on a uniquely large dataset, indicates that there are different social class correlates for colon and rectal cancer. Consequently the two sites should not be combined in studies considering lifestyle factors in the aetiology of these neoplasms.