IDO1 and nasopharyngeal carcinoma: Two-group analysis revealed a higher expression of immune markers such as CD20, CD3, CD56 FOXP3, and Ki-67 as well as ICs such as PD-1, ICOS, and IDO1 in AOIs of ‘inflamed’ NPC cf. ‘immune-excluded’ and increased expression of proteins associated with antigen presentation HLA-DR, CD40, and CD80 cf. ‘desert’ NPC (Mann–Whitney test, p-value < 0.05) (Figure 2d,f).