Tryptophan metabolism was one of the 27 pathways (Fig. 5f), and the downstream target genes of AhR, CYP1A1 and CYP1B1, were considerably elevated after AhR binding (Supplementary Fig. S25c), suggesting that tryptophan metabolism is significantly activated in recurrent castration-resistant prostate cancer. This evidence concerns the gene AHR and prostate cancer.