AHR and breast cancer: It should also be noted that microbial sensing through the AhR may have opposite effects in malignant compared to normal intestinal stem cells: in fact, AhR stimulation by formate-producing F. nucleatum activates Wnt and increases CSC-like features in colorectal cancer cells [50], and a similar pro-malignant effect of AhR ligands has been reported in the breast cancer cell line MCF-7 [137].