Furthermore, we performed correlation studies in the TCGA database and observed a positive correlation between IDO1 (r = 0.87, p < 0.001), IDO2 (r = 0.70, p < 0.001), TDO2 (r = 0.63, p < 0.001), and IL4I1 (r = 0.53, p < 0.01) with PD‐L1 expression in DLBCL (Figure 2D). This evidence concerns the gene IDO2 and diffuse large B-cell lymphoma.