A recent study unveils that Bacterium Fusobacterium nucleatum induces formate secretion to activate the AhR signaling pathway, leading to enrichment of cancer stem cells.11 In contrast, Lactobacillus plantarum (LP) supernatant inhibits the expression of particular CSC markers, sphere formation capacity and boosts 5-fluorouracil (5-FU) drug sensitivity in colorectal cancer cells.12,13 Although emerging studies verify that gut microbiota-derived secondary metabolites regulate a series of CSC properties, the molecular mechanisms of cancer stemness regulated by gut bacteria are poorly understood. Here, AHR is linked to cancer.