Abstract
Tryptophan (TRP) metabolism occurs by kynurenine pathway (KYN pathway) and by serotoninergic pathway (SER pathway). KYN pathway generates kynurenine (KYN) and a lot of secondary products and, when it is conducted by indoleamine 2,3 dioxygenase enzyme (IDO), it contributes to tolerance phenomena and tumor cells immune escape. SER pathway produces serotonin (SER) which can generate melatoni…