Background: Hormone replacement therapy (HRT) increases the risk of breast cancer, but the association may vary according to patient factors. We investigated the association between HRT and breast cancer in a nationwide cohort with risk stratification according to risk factors for breast cancer.
Methods: Using the Korean National Health Insurance Service database, 4,558,376 postmenopausal women who underwent breast cancer screening and regular health checkups from 2009 to 2014 were analyzed.
Results: A total of 696,084 (15.3%) women reported current or previous HRT use. Breast cancer was newly diagnosed in 26,797 (0.6%) women during a median follow-up of 5.35 years. The HR of the risk of breast cancer in HRT users was 1.25 [95% confidence interval (CI), 1.22-1.29] compared with HRT nonusers. The risk of breast cancer increased according to HRT duration [adjusted HR = 1.08; 95% CI, 1.04-1.12, for <2 years; adjusted HR = 1.33; 95% CI, 1.25-1.40, for 2 to <5 years; and adjusted HR = 1.72; 95% CI, 1.63-1.82, for ≥5 years). The effects of HRT on breast cancer risk applied to both invasive and in situ cancer. The HRT-related risk of breast cancer was higher in women who were leaner and those who had dense breasts.
Conclusions: This nationwide population-based study confirms the association between HRT use and breast cancer risk. The risk increased proportionally with duration of HRT and differed according to body weight and breast density.
Impacts: Risk stratification would be useful when deciding whether to apply HRT for relief of menopausal symptoms.
©2020 American Association for Cancer Research.