Increased dopamine production in patients with carcinoid tumors

Although both carcinoid tumors and pheochromocytomas arise from neural crest origin, they are thought to each secrete distinctive monoamines; carcinoid tumors, which contain tryptophan hydroxylase, secrete serotonin, and pheochromocytomas, which contain tyrosine hydroxylase, may secrete dopamine (DA), norepinephrine (NE), or epinephrine (E). The purpose of this study was to determine if patients with carcinoid tumors have evidence of increased DA production. Of patients with serotonin-producing carcinoid tumors, 18%, 27%, and 35%, respectively, had increased urinary homovanillic acid (HVA) excretion (the principal metabolite of DA), urinary DA excretion, and plasma DA concentration. In contrast, none of the patients with nonserotonin-producing carcinoid tumors had evidence of increased DA production. Only 4% of patients with miscellaneous tumors had increased excretion of homovanillic acid or DA; none of the patients with miscellaneous tumors had increased plasma DA concentration. This study suggests that DA and HVA measurements may be useful in the evaluation of some patients with suspected carcinoid tumors.