PDCD1 and neoplasm: Culture-free methods to taxonomically profile fecal microbiomes have progressed from low-resolution 16S rRNA gene sequencing to high-resolution shotgun metagenomics, with studies of clinical cohorts finding associations between baseline Akkermansia muciniphila (lung cancer)10–13 and Faecalibacterium prausnitzii (melanoma)14–16 fecal abundances and tumor responses among anti-PD-1 recipients.