Moreover, the expression patterns of PD-1 axis are varying in different tumors: the positive rates of PD-L1 and PD-L2 in lung adenocarcinoma are about 50% [14]; PD-L1 and PD-L2 expressions are observed in 9.4 and 49.6% of renal cell carcinoma patients, respectively [15]; in metastatic melanomas, positive rates of PD-L1 and PD-1 are 49 and 25%, respectively [17]; high expressions of PD-L1 and PD-1 are detected in 38.4 and 50% of colorectal cancer patients, respectively [19]. Here, PDCD1LG2 is linked to metastatic melanoma.