Abstract
BACKGROUND: Previous systematic reviews naïvely combined biased effects of screening radiography or endoscopy observed in studies with various designs. We aimed to synthesize currently available comparative data on gastric cancer mortality in healthy, asymptomatic adults by explicitly classifying the screening effects through study designs and types of intervention effects. METHODS: We searched multiple databases through October 31, 2022 for this systematic review and meta-analysis. Studies of any design that compared gastric cancer mortality among radiographic or endoscopic screening and no screening in a community-dwelling adult population were included. The method included a duplicate assessment of eligibility, double extraction of summary data, and validity assessment using the Risk Of Bias In Non-randomized Studies of Interventions tool. Bayesian three-level hierarchical random-effects meta-analysis synthesized data corrected for self-selection bias on the relative risk (RR) for per-protocol (PP) and intention-to-screen (ITS) effects. The study registration number at PROSPERO is CRD42021277126. FINDINGS: We included seven studies in which a screening program was newly introduced (median attendance rate, 31%; at moderate-to-critical risk of bias), and seven cohort and eight case-control studies with ongoing screening programs (median attendance rate, 21%; all at critical risk of bias); thus, data of 1,667,117 subjects were included. For the PP effect, the average risk reduction was significant for endoscopy (RR 0.52; 95% credible interval: 0.39-0.79) but nonsignificant for radiography (0.80; 0.60-1.06). The ITS effect was not significant for both radiography (0.98; 0.86-1.09) and endoscopy (0.94; 0.71-1.28). The magnitude of the effects depended on the assumptions for the self-selection bias correction. Restricting the scope to East Asian studies only did not change the results. INTERPRETATION: In limited-quality observational evidence from high-prevalence regions, screening reduced gastric cancer mortality; however, the effects diminished at a program level. FUNDING: National Cancer Center Japan; and Japan Agency for Medical Research and Development.