Mammographic Breast Density and Risk of Ovarian Cancer in Korean Women

Background: This study aimed to investigate the potential association between mammographic breast density and ovarian cancer risk.Methods: This retrospective cohort study included women >= 40 years of age who underwent a mammography screening from 2009 to 2014. Breast density was assessed using the Breast Imaging-Reporting and Data System. The primary outcome was ovarian cancer development, and the cases were recorded until 2020. Cox proportional hazards regression was used to assess the association between breast density and ovarian cancer development. Subgroup analyses stratified by age, menopausal status, and body mass index (BMI) were conducted.Results: Of the 8,556,914 women included in this study, 9,246 ovarian cancer events were recorded during a median follow-up period of 10 years (interquartile range, 8.1-11.0 years). Compared with women with almost entirely fat density, those with scattered fibroglandular density, heterogeneous density, and extreme density had an increased risk of ovarian cancer with adjusted HRs of 1.08 [95% confidence interval (CI), 1.02-1.15], 1.16 (95% CI, 1.09-1.24), and 1.24 (95% CI, 1.15-1.34), respectively. The strongest association was observed in the >= 60 years age group; subgroup analysis indicated a significant increase in association between the higher-density category and ovarian cancer risk, regardless of BMI or menopausal status.Conclusions: Higher levels of breast density are associated with an increased risk of ovarian cancer.Impact: Breast density may have a relationship with ovarian cancer risk and could be used to assess future risk.