Based on these observations, we could hypothesize that therapies targeting the kynurenine immune-suppressive effect (i.e. the indoleamine 2,3-dioxygenase (IDO) inhibitor but also interferon-α-based, interlekin-2-based and more recently anti-PD1 based immunotherapies)10,39 may have a lower success rate in papRCC and chorRCC than in ccRCC. Here, IDO2 is linked to nonpapillary renal cell carcinoma.