Selection criteria

The inclusion criteria were as follows: (a) a cohort study with original data provided, including hazard ratio (HR), relative risk (RR), incidence rate ratio (IRR), standardized incidence ratio (SIR), and the corresponding 95% confidence intervals (CIs), or data sufficient to compute these measures; (b) the exposure factor was gallstones or cholecystectomy; and (c) the outcome of interest was the development of pancreatic cancer. The exclusion criteria were as follows: (a) case reports/series, letters, reviews, guidelines, protocols, replies and cross-sectional studies; (b) studies that did not precisely report HRs, RRs, IRRs, SIRs and 95% CIs for the outcome; (c) studies with no original data or whose data were not calculable for the outcome; and (d) studies limited to specific populations, such as males or females only or diabetes patients.

The titles and abstracts of the selected literature were separately screened by two authors (Na Sun and Jichao Wei). Discrepancies in the review process were verified by the senior author (Jichao Wei). The remaining articles were separately screened through a comprehensive reading of the full text. The reference lists of articles deemed relevant during the full-text review process were cross-checked to identify any additional relevant studies.