The microbiome may play an important role in modulating immune system function and new pre-clinical research is suggesting that commensal bacteria of the gut may have an effect in cancer prognosis. Specific bacterial species in combination with immunotherapy has been recently shown to boost the ability of the immune system to recognize and attack cancer cells, specifically in colorectal, melanoma, and bladder cancer cells in a mice-model (1). Three bacterial species, Bifidobacterium pseudolongum, Lactobacillus johnsonii and Olsenella species, significantly enhanced the efficacy of immune checkpoint inhibitors in mice models of cancer. These bacteria have been found to produce the metabolic metabolite inosine. This metabolite enhances the ability of T-cells to detect and attack tumor cells.