Characteristics relating to ovarian cancer risk: collaborative analysis of 12 U.S. case-control studies. VI. Nonepithelial cancers among adults. Collaborative Ovarian Cancer Group.

Nonepithelial ovarian cancers are rare, and little is known about their etiology. Of particular interest are the effects of oral contraceptive use and pregnancy, both of which are associated with large decreases in risk for epithelial ovarian cancer. We examined the risk factors for nonepithelial ovarian tumors by combining data from four case-control studies conducted in the United States. We compared personal characteristics of 38 germ cell cases and 45 stromal cases, respectively, with 1,142 and 2,617 general population controls. All subjects were over age 18 years. For germ cell tumors, there was a weak negative association with parity but no consistent pattern of decreasing risk with increasing parity. In contrast, relative to nulligravid women, gravid nulliparous women were at increased risk of developing a germ cell cancer [odds ratio (OR) = 4.8, 95% confidence interval (CI) = 1.2-18.6]. The use of oral contraceptives was also associated with elevated risk (OR = 2.0, 95% CI = 0.77-5.1); however, no clear trends in risk were observed. For stromal tumors, oral contraceptive use was associated with decreased risk (OR = 0.37, 95% CI = 0.16-0.83), whereas pregnancy was associated with a small elevation in risk. A trend of increasing risk with increasing age at first term pregnancy was observed, with an odds ratio of 3.6 (95% CI = 1.0-12.5) for a first birth after age 29 years. Risk factors for nonepithelial ovarian cancers do not appear to parallel each other or those for epithelial ovarian cancer.