IDO1 and diffuse large B-cell lymphoma: A significant correlation was not observed between IDO1, IDO2, TDO2, IL4I1, and PD‐L1 expression and clinical characteristics in DLBCL or NK lymphoma; however, PD‐L1 (p < 0.001), IDO1 (p < 0.001), and IDO2 (p = 0.003) were expressed at a higher proportion in NK/TCL than in DLBCL, whereas TDO2 often exhibited higher expression levels in DLBCL than in NK/TCL (p = 0.003) (Figure 1B).