IDO1 and neoplasm: Dietary tryptophan restriction, blockade of the key rate-limiting enzyme IDO1 of tryptophan metabolism, or inhibition of cellular tryptophan import also contribute to the inhibition of tumor progression, suggesting that tryptophan metabolism plays an important role in chemotherapy resistance in bladder cancer, which provides a new perspective for the development of therapeutic strategies for bladder cancer targeting the tryptophan metabolism pathway 187.