Association of menopausal hormone therapy with gastric and colorectal cancer risks in Korean women: A nationwide population-based cohort study.

Background: Menopausal hormone therapy (MHT) has been associated with a decreased risk of gastric cancer (GC) and colorectal cancer (CRC); however, few studies have been conducted in diverse ethnic groups, particularly in the Asian population. Therefore, the current study evaluated if MHT is inversely associated with GC and CRC in East Asia using a representative population-based study in Korea.

Methods: This retrospective cohort study was conducted using the National Health Insurance Service-National Sample Cohort 2.0 in South Korea from 2002 to 2015. A total of 196,095 women aged ≥40 years were included in the study. The numbers of participants who did and did not use MHT were 19,063 (9.7 %) and 177,032 (90.3 %), respectively. Hazard ratios (HRs) and the corresponding 95 % confidence intervals (CIs) were estimated using a time-dependent Cox proportional hazards model. Age was considered as a time scale, and other confounding factors, including income levels based on insurance premiums, region of residence, and comorbidities, were included in the multivariable-adjusted model.

Results: The total number of incident cases of GC and CRC were 1339 (0.68 %) and 1428 (0.73 %), respectively. We observed an inverse association of the use of estrogen replacement therapy (ERT; estrogen-containing therapy regardless of other regimen types) with GC [HR (95 % CI):0.68 (0.51-0.90)], CRC [0.57 (0.42-0.78)] and gastrointestinal cancer [GI, 0.63 (0.51-0.77)]. In the analyses by CRC subsite, the risks of both colon and rectal cancers were associated with ERT. In addition, both estrogen and combined estrogen and progestogen regimens were significantly associated with CRC and GI cancer.

Conclusion: ERT was associated with a decreased risk of GC and CRC. Our findings support the protective effect of estrogen against GC and CRC in Korean women.