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 more 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 July 1999 (n = 767) were compared with community controls (n = 1,367). Compared with never users, the adjusted risk of ovarian cancer was reduced by 40% for oral contraceptive users overall, with longer duration of use affording greater protection. The ovarian cancer risk reduction was similar for women who initiated oral contraception before 1972, when high-dose pills dominated the market; between 1972 and 1980; and after 1980, when newer, lower-dose pills dominated. Oral contraceptive estrogen and progestin content were compared for cases and controls after adjustment for current age, number of pregnancies, race, and family history of ovarian cancer. Use of low-estrogen/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).