Association of hormone replacement therapy with risk of gastric cancer: a systematic review and meta-analysis.

Hormone replacement therapy (HRT) is widely used to relieve menopausal symptoms; however, it remains unclear whether the use of HRT was associated with gastric cancer. We conducted a systematic review and meta-analysis to synthesize available evidence. This study followed the PRISMA guideline to report meta-analysis. PubMed, Embase, and Cochrane library were searched from conception through 23 February 2022. Eligible studies reporting risk of gastric cancer after HRT were screened and accessed by two independent reviewers. Random-effects meta-analysis was used to calculate pooled risk estimate as relative risk (RR, 95% CI). Pre-established review protocol was registered in PROSPERO (CRD42021281260). Among the 1095 articles identified, we included 11 studies with 1,919,089 women in this meta-analysis. The combined risk estimate (RR, 0.72; 95% CI 0.64-0.81; I = 2%) indicated that the use of HRT was associated with a 28% reduction in risk of gastric cancer compared with those who had no HRT exposure. The narrow prediction interval (0.62-0.84) for gastric cancer risk suggested a low between-study variance. In subgroup analysis defined by HRT formulation, there were reduction in risks of gastric cancer after the use of estrogen-only therapy (Pooled RR, 0.63; 95% CI 0.51-0.77, I = 0%) and estrogen-progestin therapy (Pooled RR, 0.70; 95% CI 0.57-0.87; I = 0%), as compared with non-users. In this systematic review and meta-analysis, the use of HRT was associated with a reduced gastric cancer risk regardless of HRT formulation. Further investigations are warranted to confirm underlying mechanisms.