Case-control study of borderline ovarian tumors: reproductive history and exposure to exogenous female hormones.

Borderline ovarian tumors possess many of the same morphological features as their malignant counterparts, but they do not destructively invade the ovarian stroma, and the women in whom they develop generally have a favorable prognosis. Female residents of three urban counties of western Washington diagnosed with serous and mucinous borderline ovarian tumors between 1980 and 1985 (n = 116) were interviewed regarding past reproductive events. A random sample of women from the same counties (n = 158) was identified through random digit dialing and were interviewed. The risk of these ovarian tumors among women who had given birth to 1 or 2 children and to 3 or more children was, respectively, 0.7 and 0.4 that of nulliparous women. There was no consistent influence of increasing age at first live birth. Adjusting for parity, a history of lactation was associated with a 50% reduction in risk. Among nulliparous women, a further increase in risk was present in those who reported a history of infertility. Use of oral contraceptives was associated with a 60% reduction in risk. However, the size of the association was not dependent on duration, age at first use, or years since last usage. In conclusion, borderline tumors appear to have similar epidemiological patterns with regard to reproductive events as their more malignant counterparts.