Substance P in the localization of a carcinoid tumor

A 55‐year‐old woman with an ovarian carcinoid presented with intermittent facial and cervical flushing for 10 years, watery diarrhea for 4 years, and abdominal pain without hepatomegaly. Markedly elevated systemic venous and arterial serotonin levels (830 ng/ml; nl = 50‐200 ng/ml) were found. The highest serotonin levels were observed in the superior venal caval system, but serotonin as a marker for tumor localization was inaccurate and led to an unproductive neck exploration. The histological pattern of this tumor contained purely insular elements. No hepatic or nodal metastases were identified and the lesion was unilateral. Substance P levels were elevated in the venous drainage of the left ovary and in retrospect correctly localized the ovarian tumor. This peptide may prove to be another carcinoid tumor marker in addition to serotonin and 5‐hydroxyindolacetic acid. Substance P may also be an important mediator of symptoms in patients with carcinoid syndrome.