Elevated expression of tryptophan-2,3-dioxygenase 2 (TDO2) and indoleamine 2,3-dioxygenase 1 (IDO1) enhances kynurenine (Kyn) production, which fosters PCa progression through tumor-associated immunosuppression and direct pro-survival signaling (52–54). Here, TDO2 is linked to neoplasm.