IDO1 and diffuse large B-cell lymphoma: However, IDO1, IDO2, TDO2, and IL4I1 positivity did not significantly differ between PD‐L1+ and PD‐L1− biopsy tissue samples of NK/TCL; nonetheless, a positive correlation of 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 < 0.05) with PD‐L1 expression was observed in the TCGA‐DLBCL dataset.