Risk Factors for Epithelial Borderline Ovarian Tumors: Results of a Swedish Case–Control Study

OBJECTIVE: Borderline ovarian tumors have a favorable prognosis. Previous epidemiological studies indicate common risk factors for invasive epithelial ovarian cancers and borderline tumors, but it remains unresolved whether these tumors are precursors of invasive cancers or a separate disease entity. The objective of this population-based case-control study conducted in 1993-1995 was to examine reproductive and other factors in relation to the risk of borderline ovarian tumors. METHODS: Subjects were 193 histologically verified incident epithelial borderline tumor cases and 3899 randomly selected controls aged 50-74 years, whose data were collected through mailed questionnaires. Risk estimates were calculated by unconditional logistic regression. RESULTS: Ever parous women were at reduced risk, with odds ratios of 0.44 (95% confidence interval (CI) 0.26-0.75) for serous and 0.63 (95% CI 0.34-1.19) for mucinous tumors. No clear trends emerged for age at first birth, at menarche, and at menopause. Lactation reduced tumor risk. Oral contraceptive ever use conferred no protection, with odds ratios of 1.40 (95% CI 0.87-2.26) for serous and 1.04 (95% CI 0.61-1.79) for mucinous tumors. The odds ratio for serous tumors following unopposed estrogen ever use was 2.07 (95% CI 1.08-3.95), whereas no risk increase appeared with estrogens supplemented by cyclic or continuous progestins. Mucinous tumors were not associated with hormone replacement therapy. The odds ratio for serous tumors in the highest category of body mass index was 6.47 (95% CI 3.09-13.5). CONCLUSIONS: Increasing parity and lactation reduce the risk of borderline ovarian tumors in women aged 50-74, while no protection follows oral contraceptive use. Hormonal situations such as unopposed estrogen use and obesity, where estrogens are not counteracted by progestins, may increase the risk of serous tumors.