PDCD1 and neoplasm: ICOS mRNA expression in those whole tumor samples strongly correlated with mRNA expression of other therapeutically relevant immune checkpoint genes, i.e. PD-L1 (ρ = 0.704, P < 0.001), PD-1 (ρ = 0.843, P < 0.001), PD-L2 (ρ = 0.800, P < 0.001), CTLA4 (ρ = 0.586, P < 0.001), LAG3 (ρ = 0.817, P < 0.001), and TIGIT (ρ = 0.906, P < 0.001) (Fig. 1B).