To evaluate the relation between oral contraceptives and colon and rectal cancer, we analyzed combined data from two case-control studies conducted in six Italian regions between 1985 and 1996. The studies included 803 women with incident colon cancer, 429 with rectal cancer, and 2,793 controls with acute, nonneoplastic, nondigestive, non-hormone-related disorders. We estimated odds ratios (ORs) and 95% confidence intervals (CIs) from unconditional multiple logistic regression equations, including terms for age, center/study period, education, family history of colorectal cancer, menopausal status, age at menopause, parity, use of hormone replacement therapy, body mass index [weight (kg) per height squared (m2)], and total energy intake. Ever-use of oral contraceptives was inversely associated with colon cancer (OR = 0.63; 95% CI = 0.45-0.87) and rectal cancer (OR = 0.66; 95% CI = 0.43-1.01). Duration of use of oral contraceptives was inversely related to risk of colon but not rectal cancer. This study suggests that women who have ever used oral contraceptives are at lower risk of colon and rectal cancer.
PIP: The 15 cohort and case-control studies published to date on the association between oral contraceptive (OC) use and colorectal cancer have yielded conflicting results; 7 revealed a reduced cancer risk among OC users, 6 showed no association, and 2 reported some increased risk. The present analysis combined data from a multicenter case-control study, conducted in 6 Italian regions in 1992-96 with data from a 1985-91 study in northern Italy, yielding a total of 803 women with colon cancer (median age, 61 years), 429 cases of rectal cancer (median age, 62 years), and 2793 controls (median age, 57 years). 59 women with colon cancer (7.3%) and 323 controls (11.6%) reported ever-use of OCs (odds ratio (OR), 0.63; 95% confidence interval (CI), 0.45-0.87). OC use for more than 24 months further decreased this risk (OR, 0.52; 95% CI, 0.32-0.85). The protection conferred by OC use was similar when the origin of the neoplasm was in the ascending, transverse, or descending colon. An inverse association was also found between ever-use of OCs and rectal cancer (OR, 0.66; 95% CI, 0.43-1.01), but there was no association with duration of OC use. For colon and rectal cancers combined, a 36% reduction in cancer risk was present among ever-users of OCs (OR, 0.64; 95% CI, 0.49-0.85). These findings are consistent with the descriptive epidemiology of colorectal cancer, the bile acid hypothesis, and experimental findings on estrogen receptors and the colorectal cancer pathway.