The effect of menopausal hormone therapy on gastrointestinal cancer risk and mortality in South Korea: a population-based cohort study

Background: The effect of menopausal hormone therapy (MHT) on gastrointestinal (GI) cancers is controversial, and no research has been conducted in the East. This study investigates the association between MHT and GI cancer risks in South Korea. Methods: A prescription-based cohort study was conducted using the NHIS Sample Cohort (2002–2013) of Korea. We used 1:5 propensity score matching, and 22,577 MHT users and 111,113 non-users were selected. Kaplan–Meier survival curves with log-rank tests were used. Cox proportional hazard models were used to estimate hazard ratios (HR) with 95% confidence intervals (CI). Landmark analysis was used to determine dose–response relationship. Results: The median follow-up was 79.6 of months. Kaplan–Meier survival curve showed less frequent GI cancer diagnoses in MHT users compared to non-users (0.13 vs. 0.16 per 100,000 person-years). Menopausal hormone therapy was associated with decreased incidence of GI cancer (HR = 0.809, 95%CI = 0.691–0.946) and colorectal cancer (CRC) (HR = 0.757, 95%CI = 0.577–0.995). Gastric cancer (GC) incidence showed marginal significance (HR = 0.787, 95%CI = 0.605–1.023). The mortality from GI cancer was lower in MHT users than in non-users (HR = 0.737, 95%CI = 0.547–0.993). The relationship between MHT and GI cancer was stronger with increasing MHT dose in terms of both incidence (P_trend = 0.0002) and mortality (P_trend = 0.0064). Conclusions: The association between MHT use and reduced risks of GI cancers was attributed to CRC and GC and showed a dose–response relationship in a population-based cohort study.