CD274 and breast cancer: As noted in Fig 2, positive PD-L1 expression significantly associated with enhanced total mortality risk (MR) among breast cancer patients in the random-effects model; the pooled RR was 1.64 (95% CI, 1.14–2.34), despite the presence of heterogeneity among the studies (I2 = 85%, p < 0.0001; Fig 2A).