Statistical Analysis
All statistical analyses were carried out on Comprehensive Meta-Analysis software (version 3.3.070, Biostat Inc, New Jersey, USA). P<0.05 was considered statistically significant. The pooled HRs for PFS and OS were calculated to evaluate the effect of PPIs exposure on ICIs therapy compared to non-PPIs users. The pooled HR>1.0 indicated an adverse influence of PPIs exposure undergoing ICIs therapy. HR<1.0 denoted a beneficial influence of PPIs exposure undergoing ICIs therapy. The χ2-based Q test and I2 statistic were applied to detect and quantize heterogeneity (18, 19). I2>50% (I2 <25%: no heterogeneity; I2 = 25–50%: moderate heterogeneity; I2 >50%: large heterogeneity) and/or P <0.1 for Q test represented statistically significant heterogeneity, in this situation, the random model was used, in other cases, fixed models were applied. We use funnel plot and Egger’s test as well as Begg’s test to detect publication bias. Publication bias is suspected if p<0.05 for the Egger’s and Begg’s tests(20, 21). Sensitivity analysis were conducted using one study removed to assess stability of pooled outcome of HR.