Hormone Replacement Therapy, Breast Cancer Risk Factors, and Breast Cancer Risk: A Nationwide Population-Based Cohort Available to Purchase

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.

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.

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.

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.

Risk stratification would be useful when deciding whether to apply HRT for relief of menopausal symptoms.