Interestingly, studies in melanoma, NSCLC, metastatic urothelial carcinoma and metastatic renal cell carcinoma have shown that resistance to PD-1/PD-L1-blocking immunotherapies correlates with increased serum levels of IL-8 [210,211,212,219,220], suggesting that IL-8 might serve as a biomarker predictive of resistance to PD-1/PD-L1-blocking therapies. This evidence concerns the gene CXCL8 and melanoma.