Association of Reproductive Factors, Oral Contraceptive Use and Selected Lifestyle Factors with the Risk of Ovarian Borderline Tumors: A Danish Case-control Study

Objective The aim was to examine risk factors for ovarian borderline tumors overall, and according to histological subtype (serous vs. mucinous), in a large Danish population-based case-control study. Methods Ovarian borderline cases and controls were recruited from 1995 to 1999, and personal interviews were conducted. In all, 202 cases and 1,564 randomly selected controls were included. The analysis was performed using multiple logistic regression models. Results The risk of ovarian borderline disease decreased with increasing parity (OR=0.79 per birth, 95% CI: 0.63–0.98) and older age at first birth (OR=0.67 per 5 years, 95% CI: 0.53–0.84). Both a history of breastfeeding and use of oral contraceptives reduced the risk of borderline tumor, the effect being most pronounced for serous tumors. Increasing body mass index (BMI) was associated with elevated risk of serous borderline tumor (OR=1.05 per BMI unit; 95% CI: 1.00–1.10), whereas current smoking was a strong risk factor only for mucinous tumors (OR=2.10; 95% CI: 1.22–3.60). Finally, increasing consumption of milk (all types) was found to increase the risk of borderline disease (OR=1.04 per glass milk per week; 95% CI: 1.02–1.06), and increasing intake of total lactose also increased the risk significantly (OR=1.16 per 50 gram lactose per week; 95% CI: 1.06–1.26). Conclusion The risk profile of ovarian borderline tumors is similar to that of ovarian carcinomas, and we observed significant etiological differences between serous and mucinous borderline tumors.