SPP1 and prostate cancer: The heterogeneity of the obtained results is low (P=0.25, I2 = 26%), so the fixed-effects model is adopted and showed that the expression of OPN in PCA tissues was significantly higher than that in normal prostate cancer tissues (OR = 46.55, 95% CI [12.85, 168.59], P<0.00001) (Figure 3A).