Possible relationships between tubal ligation and hysterectomy and epithelial ovarian cancer were assessed in data that were collected for a multinational hospital-based case-control study conducted between 1979 and 1988. Histologically confirmed incident cases (n = 393) were compared with controls (n = 2563) matched on age, hospital, and year of interview. A nonsignificant reduction in risk was observed for tubal ligation [odds ratio (OR), 0.72; 95% confidence interval (CI), 0.48-1.08] and hysterectomy (OR, 0.58; 95% CI, 0.26-1.27). There was no trend in risk with time since tubal ligation. The possible protective effect of tubal ligation was greatest in women of parity less than four. The apparent protective effect of tubal ligation was seen only for clear cell (OR, 0.32; 95% CI, 0.006-2.50) and endometrioid (OR, 0.20; 95% CI, 0.046-1.46) tumors, suggesting a hormonal mechanism for the observed associations.

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