Reproductive, genetic, and dietary risk factors for ovarian cancer.

A case-control study of 110 women with ovarian epithelial carcinoma and 220 individually age-matched controls was conducted in Hokkaido, Japan, to identify ovarian cancer risk factors. Both the cases and the matched controls were surveyed either from 1980 to 1981 or from 1985 to 1986. Ovarian cancer risk was increased in single women (p less than 0.01), and in women with a family history of breast, uterine, or ovarian cancer in a mother or sister (p less than 0.001). Conversely, risk was decreased in women who had experienced a livebirth (p less than 0.001), an induced abortion (p less than 0.05), or who had had permanent sterilization by tubal ligation (p less than 0.05). Each of the reproductive factors remained significant when adjusted for each other using logistic regression analysis. The odds ratio for ovarian cancer decreased significantly with increasing number of livebirths (p less than 0.001). Furthermore, a significant negative association between anovulatory periods and ovarian cancer risk was noted (p less than 0.01). No association was observed for any types of contraceptive methods other than tubal ligation, but the prevalence of oral contraceptive use was very low. A significant positive association with daily fish consumption (p less than 0.05) and a marginally significant negative association with daily milk consumption (p = 0.05) were also observed.