PDCD1 and metastatic melanoma: Matson et al. reported that the fecal microbiota of metastatic melanoma patients who responded to PD-1 blockade contained higher abundances of Enterococcus faecium, Collinsella aerofaciens, Bifidobacterium adolescentis, Bifidobacterium longum, Klebsiella pneumoniae, Veillonella parvula, and Parabacteroides merdae.