Co-expression of IDO1 and PD-L1 in lung squamous cell carcinoma: Potential targets of novel combination therapy

•We examined the clinical significance of IDO1/PD-L1 co-expression in lung SCC.•IDO1 expression was significantly associated with PD-L1 expression.•IDO1/PD-L1 co-expression was significantly associated with high TILs.•Ki-67 index was significantly higher in patients with IDO1/PD-L1 co-expression.•IDO1/PD-L1 co-expression was significantly associated with shorter OS.