Tryptophan and carcinogenesis: review and update on how tryptophan may act

This review covers the historical developments of the consideration that tryptophan may influence the induction of cancer in experimental studies. Studies relating to stimulatory effects, as well as to inhibitory effects, of tryptophan or tryptophan-related compounds are described. Also the effects of pyrolysis products of tryptophan on carcinogenesis are covered. In consideration that new L-tryptophan-related contaminants may be involved in a recently described human disease, a description is given of the eosinophilia-myalgia syndrome, which has been attributed to the ingestion of L-tryptophan-containing related contaminants. Whether these new L-tryptophan-related contaminants alone or together with L-tryptophan may prove to be carcinogenic remains to be determined. Lastly, recent developments relating to regulatory effects of L-tryptophan on liver metabolism are reviewed and then considered as possibly playing a role in carcinogenesis.