RESUMO
BACKGROUND: Women with a family history of breast and/or ovarian cancer have an increased ovarian cancer risk. Yet it remains uncertain if common ovarian cancer risk factors-especially those which are modifiable-affect this high-risk population similarly to the general population. METHODS: Using the Danish and Swedish nationwide registers, we established two nested case-control study populations in women with a family history of breast and/or ovarian cancer (2,138 ovarian cancers, 85,240 controls) and women without (10,730 ovarian cancers, 429,200 controls). The overall and histology-specific associations were assessed with conditional logistic regression. The country-specific estimates were combined based on a fixed-effect assumption. RESULTS: Multiparity, hysterectomy, tubal ligation, salpingectomy, and oral contraceptive (OC) use were associated with a reduced risk of ovarian cancer in both women with and without a family history, while endometriosis and menopausal hormone treatment (MHT) were associated with increased risk. Multiparity and OC use presented protective effects across all histologic subtypes except mucinous ovarian cancer which was not associated with OC use. MHT increased the risk of serous ovarian cancer but decreased the risk of the mucinous and clear cell cancers. Endometriosis was especially related to an increased risk of endometrioid and clear cell ovarian cancer. CONCLUSION: Factors associated with a decreased ovarian cancer risk were similar between women with and without a family history of breast and/or ovarian cancer. Given the higher baseline risk for women with a family history, special attention should be paid to risk factors like endometriosis and nulliparity in this high-risk population.