Background: Patients with breast cancer who have mutations in the high penetrance genes BRCA1 and BRCA2, have an increased risk of ovarian cancer. Because these mutations are rare, easily obtained information such as age and family history of breast or ovarian cancer might be preferable for assessment of ovarian cancer risk in clinical practice.
Methods: We linked data from the Swedish Cancer Register to the Swedish Generation Register and generated a cohort of 30552 breast-cancer patients born after 1931, with information on breast and ovarian cancer diagnosis from 146117 first-degree relatives. Standardised incidence ratios (SIRs) with 95% CIs were calculated with nationwide rates of ovarian cancer, adjusted for age and calendar year.
Findings: During a mean follow-up of 6 years, 122 incident ovarian cancers were identified in the cohort, yielding an overall SIR of 2.0 (95% CI 1.6-2.4). The risk was higher in breast-cancer patients diagnosed before the age of 40 years, with a family history of breast cancer (5.6; 1.8-13.1) or ovarian cancer (17.0; 3.5-50.0). A consistently increased risk was noted in patients with a relative who was diagnosed before the age of 50 years, with either breast or ovarian cancer. Women with a family history of ovarian cancer have an almost 10% risk of developing ovarian cancer before the age of 70.
Interpretation: In young women with breast cancer, the risk of ovarian cancer is greatly raised when a family history of breast or ovarian cancer is present. Close medical surveillance, and perhaps even prophylactic oophorectomy, might be justified in high-risk groups.