Risk factors for epithelial ovarian cancer in women under age 45.

Risk factors for ovarian cancer in young women were investigated using data from a case-control study conducted between 1983 and 1992 in Milan, northern Italy, on 194 women below age 45 with histologically confirmed incident cancers of the ovary and 710 controls admitted to the same network of hospitals for acute non-gynecological, nonhormonal and non-neoplastic diseases. An elevated relative risk (RR) of ovarian cancer was found among women reporting 12 or more years of education [RR 1.6, 95% confidence intervals (CI) 1.0-2.03] and belonging to the highest social class (RR 1.8, 95% CI 1.1-3.0). Women whose mothers had had ovarian cancer had a multivariate RR of 2.7 (95% CI 0.7-10.5) compared to those with no family history. Menarche above age 13 and irregular menstrual cycles were significantly protective against ovarian cancer (RR 0.6 for both risk factors). There was a significant inverse relationship with abortions, the RR being 0.6 both for spontaneous and for induced abortions, while protection of parity was not significant. Higher risks of ovarian cancer were observed in women having first or last birth when older than 30 years (RR 2.0 and 2.4, respectively, compared to those delivering under age 25). A significant trend toward an increased risk of ovarian cancer was also observed with decreasing time since last birth. Compared with women whose last birth occurred 10 or more years before diagnosis, the RR was 2.1 (95% CI 1.1-3.9) for those reporting a birth during the last 5 years. The RR for oral contraceptive users was 0.7 (95% CI 0.5-1.0) and the protection increased with duration, with RR of 0.3 (95% CI 0.1-0.7) for 5 or more years of use. This study indicates that, although the incidence of ovarian cancer is higher in older women, recognised risk and protective factors are similar below age 45. An excess risk in the few years after a term delivery is also suggested.