Pellagra, a deficiency of vitamin B3 (niacin), can be secondary to a recurrent carcinoid tumor. Carcinoid tumors produce serotonin, which is a derivative of tryptophan. However, tryptophan is also the precursor of niacin. In patients with carcinoid tumors, the tumor can be so active that most tryptophan is used for serotonin production, resulting in niacin deficiency. [1]
References
1. Richard J. Castiello, MD; Peter J. Lynch, MD. Pellagra and the Carcinoid Syndrome. Arch Dermatol. 1972;105(4):574-577. doi:10.1001/archderm.1972.01620070046016.
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