The Association Between Menopausal Hormone Therapy and Gastric and Colorectal Cancer Risk in Korean Women: A Nationwide Population-based Cohort Study

Background: Menopausal hormone therapy (MHT) has been associated with decreased risks of
gastric cancer (GC) and colorectal cancer (CRC), but not many studies have been conducted in
diverse ethnic groups, particularly in the Asian population.

Objectives: The current study evaluated whether MHT is inversely associated with GC and CRC in Korea.

Methods: This retrospective cohort study of women over 40 years was conducted using the National Health Insurance Service-National Sample Cohort in South Korea from 2002 to 2015. According to total prescription days of MHT, MHT ever users and never users were classified. Those who had been prescribed MHT over 28 days were defined as ever users, otherwise classified as never users. In addition, the estrogen-containing hormone therapy was defined as those who were prescribed estrogen-only (except for tibolone) or estrogens and progestogens therapy for more than 28 days. Hazard ratios (HR) and corresponding 95% confidence intervals (CIs) were estimated using a time-dependent Cox proportional hazards model. Age was considered as time-scale, and other confounding factors such as income-based insurance premiums, region of residence, and Charlson's comorbidity index were included in the multivariable-adjusted model.

Results: A total of 196,549 women were included, 18,440 (9.4%) and 178,109 (90.6%) were MHT ever and never users respectively. We observed an inverse association between the use of estrogen-containing hormone therapy (except for tibolone, other estrogen types) and GC [HR (95% CI): 0.74 (0.56-0.97)], CRC [0.72 (0.55-0.95)], and gastrointestinal cancer [0.73 (0.61-0.89)] has been observed. In regimen types, both of estrogen-only therapy[0.49 (0.22-1.09) in GC and 0.32 (0.12-0.85) in CRC] and estrogen and progestogen therapy [0.82 (0.57-1.17) in GC and 0.73 (0.50-1.07) in CRC] showed a decreased tendency of GC and CRC.

Conclusions: Estrogen-containing hormone therapy was associated with decreased risks of GC and CRC. There were no differences by regimen type.