PDCD1 and melanoma: The results showed that in all tumor types and melanoma patients accepted anti-PD-1 therapy, the expression of CRABP2 was significantly increased in nonresponsive group (all tumor type: p = 0.000, Fig. 2G, ROC curve in Fig. 2H; melanoma: p = 0.007, Fig. 2I, ROC curve in Fig. 2J).