IDO1 and small cell lung carcinoma: In our previous study [24], we investigated the expression pattern of 15 immune-related markers (PD-1, CD27, CD4, CD47, ICOS, LAG3, OX40, PD-L1, IDO, CD70, CD137, CD3, CD40, NKG2A, CD8) using a representative number of AC, LCNEC, and SCLC samples.