Molecular pathways linking the gut microbiome to antitumor immunity.

Accumulating evidence supports the important role played by the gut microbiota in controlling antitumor immune responses that impact tumor development. Extensive studies of bacterial species known to impact tumor growth have identified metabolites, produced by either bacteria or the host, that may alter efficacy of chemo- and/or immune-based therapies. Here, we summarize our current knowledge of those metabolites and the related bacterial species that influence activities linked with antitumor immunity, including epigenetic changes, the aryl hydrocarbon receptor signaling, cytokine and chemokine production, Janus kinase/signal transducer and activator of transcription signaling, and toll-like receptor signaling. We focus on specific metabolites, produced in the gut microbiome, which can alter molecular pathways associated with antitumor immunity, findings that warrant further evaluation in preclinical or clinical settings.