CD274 and small cell lung carcinoma: After the potential outlying studies were left out of the random-effect model, the pooled estimate of the prevalence of PD-L1 expression in SCLC was 22.0% (95% CI: 15.0–30.0) with a significant heterogeneity (I2 = 95.0, 95% CI: 91.6–97.5, p < 0.0001) (Figure S4).