Metagenomic shotgun sequencing of stool specimens of metastatic melanoma patients has shown enriched levels of Bacteroides caccae in people responsive to different immune checkpoint inhibitor treatments, including ipilimumab (anti-CTLA-4), nivolumab (anti-PD-1), a combination of ipilimumab and nivolumab, and pembrolizumab (anti-PD-1) (236). This evidence concerns the gene CTLA4 and metastatic melanoma.