Colorectal cancer: Three cohort studies (n = 717,907) showed a pooled HR of 1.31 (95% CI: 0.81–2.10; p = 0.2675), indicating no significant link with long-term PPI use. Heterogeneity was high (I² = 88%; Q = 17.37, df = 2; p = 0.0002), likely due to variation in exposure, follow-up time, and study populations. Gastric cancer: Six studies (n = 707,706) yielded a pooled HR of 1.64 (95% CI: 1.22–2.20; p = 0.001), showing a significant association. Heterogeneity was substantial (I² = 90%; Q = 52.06, df = 5; p < 0.0001), with possible sources including H. pylori prevalence, inconsistent confounder adjustment (smoking, aspirin), and outcome definition differences. Most showed a consistent risk trend. Funnel plots suggested possible publication bias in the gastric data, while fewer colorectal studies limited conclusions.


