Accumulating evidence indicates that dysregulation of microbiota-host interactions associates with various diseases, including inflammatory bowel diseases (IBDs), colorectal cancer, diabetes, and liver cirrhosis (1). Recently, research has generated paradigm shifts in concepts about the interactions between bacteria and cancer therapeutic drugs. For example, bacteria modulate the antitumor efficacy in preclinical models of various chemotherapies (2–4) and immunotherapeutic agents (5, 6). Conceptually, these findings suggest that bacteria-mediated interactions with the immune system are essential for optimal drug efficacy. However, there is limited information regarding the functional impact of the composition of the human microbiome and therapeutic outcomes in cancer patients. On pages 91, 97, and 104 of this issue, Routy et al. (7), Gopalakrishnan et al. (8), and Matson et al. (9), respectively, address this important issue and demonstrate that patients can be stratified into responders and nonresponders to immunotherapy on the basis of the composition of their intestinal microbiomes, suggesting that microbiota should be considered when assessing therapeutic intervention.
