Matson et al. found that an abundance of Bifidobacterium longum, Collinsella aerofaciens, and Enterococcus faecium was associated with anti-PD1 efficacy in metastatic melanoma patients [37], while Gopalakrishnan et al. observed higher microbial diversity and increased Ruminococcaceae levels in responding melanoma patients relative to non-responders, together with an enhanced systemic and antitumor immunity [36]. This evidence concerns the gene PDCD1 and melanoma.