Malignant melanoma producing serotonin.

A case of malignant melanoma, the tumor of which seems to produce serotonin, is presented. Neither hyperserotoninemia nor carcinoid syndrome was observed in the clinical course. An autopsied sample of the metastatic lung tumor contained a significantly higher concentration (1.35 microgram/g wet weight tissue) of serotonin than that of normal lung (below 0.5 microgram wet wt.). Tryptophan hydroxylase activity, the key enzyme of the biosynthesis of serotonin, was substantial in the same tumor sample when assayed by a sensitive radioisotopic method, supporting the productivity of the amine of the tumor. The ability of melanoma to produce serotonin could be attributed to its neural crest origin.