Personal and environmental characteristics related to epithelial ovarian cancer. I. Reproductive and menstrual events and oral contraceptive use.

In 2 case-control studies conducted in the 6-county San Francisco Bay Area 111 women diagnosed with epithelial ovarian carcinoma between 1974-77 and 188 women diagnosed between 1983-85 were interviewed concerning their menstrual sexual and reproductive histories. Controls were matched to cases by age and race. Qualitative and quantitative findings were similar for the 2 studies. In the combined data cases were more likely than their matched controls to have been nulliparous to have undergone menarche at an early age and to have refrained from using oral contraceptives (OCs). Menopause occurred slightly later for cases than for controls but the differences were not statistically significant. Neither age at 1st term pregnancy (20 or more weeks gestation) nor number of term pregnancies was predictive of ovarian cancer risk. The protection afforded by OC use was independent of parity and it increased with increasing duration of use. There were no trends in risk with time since last OC use or with time since 1st use after adjustment for duration of use. These observations suggest that OC use decreases risk for ovarian cancer rather than merely indicates fertility which may itself decrease risk of developing the disease. The authors combined reproductive characteristics and OC use to estimate a womans total duration of ovulation which was positively associated with ovarian cancer risk (p<0.001 for trend). These observations support the concept that the greater the duration of ovulation or accompanying endocrinologic phenomena the greater a womans risk for ovarian cancer. (authors)