Takada K, et al. - Researchers investigated 202 patients with surgically resected primary lung squamous cell carcinoma (SCC) to determine the prognostic impact of indoleamine 2, 3-dioxygenase 1 (IDO1)/programmed cell death-ligand 1 (PD-L1) co-expression and its association with tumor-infiltrating lymphocytes (TILs). They used immunohistochemistry to assess the expression levels of IDO1, PD-L1, Ki-67, cluster of differentiation 3 (CD3), CD4, and CD8. Findings showed a significant association of IDO1 expression with PD-L1 expression. They also observed a significant association between IDO1/PD-L1 co-expression and high TILs. The patients with IDO1/PD-L1 co-expression exhibited a remarkably higher Ki-67 index. Also, a significant association of IDO1/PD-L1 co-expression with shorter overall survival was seen. Most likely, co-expression of IDO1 and PD-L1 represent important targets for immunotherapy in lung SCC.