The published data on the relationship between the expression of several ICs—PD-L1, B7-H3, B7-H4, IDO1, Gal-3 and -9, CEACAM1, CD155, Siglec-15, and the ADAM17 immune response modulator—with the prognosis of cancer tumors, including GC, are analyzed. This evidence concerns the gene IDO1 and cancer.