Association of estrogen and progestin potency of oral contraceptives with ovarian carcinoma risk.

OBJECTIVE To estimate the association of the estrogen and progestin potency of combined oral contraceptive pills (OCPs) with epithelial ovarian carcinoma risk. METHODS This population-based case-control study included 745 women with incident, histologically confirmed epithelial ovarian carcinoma and 943 controls, matched on age and ethnicity. Data were collected using a standard questionnaire, picture albums, and calendars. The association of OCP potency with epithelial ovarian carcinoma risk was modeled using unconditional logistic regression. RESULTS When compared with women who never used hormonal contraception, users of OCPs with low estrogen (equal to or less than 0.035 mg ethinyl estradiol) and low progestin (less than 0.3 mg norgestrel) were at significantly reduced risk of ovarian carcinoma (odds ratio 0.19; 95% confidence interval 0.05-0.75). The risk among these women was lower than among users of estrogen or progestin of high potency, but the difference was not statistically significant. However, in a subset of 205 women who reported exclusive use of norethindrone, users of 0.5 mg or less, had a significantly reduced risk of ovarian cancer compared with women using 10 mg of this progestin. Increased norethindrone dose resulted in a significant increase in ovarian carcinoma risk, indicating a dose-response association. CONCLUSION Combined OCPs were effective at decreasing the risk of epithelial ovarian carcinoma, with the strongest risk reduction associated with low-potency formulations. LEVEL OF EVIDENCE II.