In melanoma patients receiving PD-1 inhibitors, a lower alpha-diversity of the gut microbiome and relative abundance of Bacteroidetes phyla was associated with shorter survival and resistance to treatment [76], whereas, pre-treatment stool samples from 42 patients with metastatic melanoma receiving anti-PD1 therapy showed more commensals such as Bifidobacterium longum, Collinsella aerofaciens, and Enterococcus faecium species in responders than in non-responders [81]. Here, PDCD1 is linked to metastatic melanoma.