Impact of progestin and estrogen potency in oral contraceptives on ovarian cancer risk.

BACKGROUND: Oral contraceptive (OC) use is associated with a reduced risk of developing ovarian cancer, but the mechanism for the risk reduction has not been well defined. In this study, we investigate the relationship between the progestin and estrogen potency in combination OCs and the risk of developing ovarian cancer. METHODS: The study included 390 case subjects with epithelial ovarian cancer and 2865 control subjects, between 20 and 54 years of age, identified from the Cancer and Steroid Hormone Study. Logistic regression was used to calculate odds ratios (ORs) and 95% confidence intervals (CIs) for the associations between ovarian cancer risk and combination OC formulations while controlling for potential confounders. All statistical tests were two-sided. RESULTS: With users of high-progestin/high-estrogen potency OC as the referent group, users of low-progestin/high-estrogen potency formulations (adjusted OR = 2.1; 95% CI = 1.2 to 3.7) and low-progestin/low-estrogen potency formulations (adjusted OR = 1.6; 95% CI = 0.9 to 3.0) had a higher risk of ovarian cancer than users of high-progestin/high-estrogen potency formulation. Low-progestin potency OC formulations were associated with a statistically significant higher risk than high-progestin potency formulations (adjusted OR = 2.2; 95% CI = 1.3 to 3.9). This association was seen even among users of short duration. CONCLUSION: The combination OC formulations with high-progestin potency appear to be associated with a greater reduction in ovarian cancer risk than those with low-progestin potency. Mechanisms underlying this reduction may include inhibition of ovulation and/or some direct biologic effects of the progestin.