Human and animal studies highlighted the role of gut microbiota by demonstrating that composition and diversity were predictive of response to ICI immunotherapy in melanoma patients; furthermore, patients with advanced non-small cell lung cancer (NSCLC), renal cell carcinoma (RCC), and urothelial carcinoma treated with PD-1/PD-L1 mAb who underwent antibiotic treatment showed significantly shorter progression-free survival (PFS) and overall survival [89]. This evidence concerns the gene PDCD1 and melanoma.