Risk of ovarian cancer in relation to estrogen and progestin dose and use characteristics of oral contraceptives

Although past studies have shown that oral contraceptives with 50 mu g or m ore of estrogen reduce the risk of ovarian cancer, it is not clear whether newer, lower-dose formulations do as well. We conducted a population-based, case-control study in the Delaware Valley to assess the impact of dose of oral contraception on risk of ovarian cancer. Cases aged 20-69 years with a diagnosis of epithelial ovarian cancer ascertained between May 1994 and Ju ly 1999 (n = 767) were compared with community controls (n = 1,367). Compar ed with never users, the adjusted risk of ovarian cancer was reduced by 40% for oral contraceptive users overall, with longer duration of use affordin g greater protection. The ovarian cancer risk reduction was similar for wom en who initiated oral contraception before 1972, when high-dose pills domin ated the market; between 1972 and 1980; and after 1980, when newer, lower-d ose pills dominated. Oral contraceptive estrogen and progestin content were compared for cases and controls after adjustment for current age, number o f pregnancies, race, and family history of ovarian cancer. Use of low-estro gen/low-progestin pills afforded an estimated risk reduction (odds ratio = 0.5, 95% confidence interval: 0.3, 0.6) that was identical to that for high -estrogen/high-progestin pills (odds ratio = 0.5, 95% confidence interval: 0.3, 0.7).