AHR and cancer: As a ligand-activated transcription factor, AHR was discovered as a receptor of 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin),35 and was reported to be highly expressed in different types of cancer, contributing to malignant phenotypes of cancer cells.36–38 Furthermore, there is study showing that AHR can transcriptionally regulate CYP enzymes.11,20,39 As supported, our study demonstrated that AHR indeed regulated CYP2S1 transcription, and further identified CYP2S1 as a potential downstream target of AHR.