Factors affecting the association of oral contraceptives and ovarian cancer.

We investigated the relation between epithelial ovarian cancer and the use of oral contraceptives in a case-control study of 144 white women under the age of 60 who had ovarian cancer and 139 white women under 60 who were selected from the general population. We observed a decreased risk for ovarian cancer associated with the use of oral contraceptives in subjects 40 through 59 years of age at the time of the study. The relative risk, adjusted for parity, was 0.11, with 95 per cent confidence limits of 0.04 to 0.33. In contrast to the findings in older women, a decreased risk for ovarian cancer associated with oral-contraceptive use was not found in women under 40. In this group, the adjusted relative risk associated with any use of oral contraceptives was 1.98, with 95 per cent confidence limits of 0.74 to 5.27. The lowest risk for ovarian cancer associated with the use of oral contraceptives was observed in older parous subjects and in women who had discontinued use more than 10 years previously.