Which of the following statements about carcinoid syndrome are true?

C. Foregut carcinoid tumors cause atypical carcinoid syndrome; hindgut tumors are rarely, if ever, associated with the syndrome.

D. The long-acting somatostatin analog provides the best symptomatic treatment for carcinoid syndrome.

DISCUSSION: Carcinoid syndrome occurs when venous drainage from the tumor gains access to the systemic circulation, escaping hepatic degradation. Although hepatic metastases are most often responsible, retroperitoneal metastases and bronchial, ovarian, and testicular carcinoid tumors can also cause the carcinoid syndrome. Serotonin is thought to be largely responsible for both the diarrhea and the fibrosing cardiac lesions associated with the carcinoid syndrome. The vasomotor changes, however, are mediated by kinins and such vasoactive peptides as substance P, neuropeptide K, neurokinin A, and neurotensin. Other substances, such as histamine, vasoactive intestinal peptide (VIP), and prostaglandins, may also contribute to systemic manifestations in the carcinoid syndrome. Foregut carcinoid tumors, of which stomach and bronchial tumors are the most common, can cause atypical carcinoid syndrome. It is thought that these tumors are deficient in the enzyme dopa-decarboxylase and have impaired conversion of 5-hydroxytryptophan (5-HTP) into 5-hydroxytryptamine (5- HT), leading to secretion of 5-HTP into the vascular compartment. Some of the 5-HTP is converted into 5-HT and 5- hydroxyindoleacetic acid (5-HIAA) in extrarenal sites, and some is decarboxylated in the kidney and excreted into the urine as 5-HT; but some of the 5-HTP is excreted directly into the urine. Thus, in patients with foregut tumors, the urine contains relatively little 5-HIAA (but more than normal) but large amounts of 5-HTP and 5-HT, in contrast to patients with midgut carcinoid tumors in which large amounts of 5-HIAA are secreted into the urine but relatively little 5-HTP. Carcinoid tumors of the hindgut contain no argentaffin or argyrophil cells, they have no secretory products, and therefore they are not associated with the carcinoid syndrome. The long-acting somatostatin analog provides the best symptomatic therapy, because somatostatin inhibits both release and action of humoral mediators of the carcinoid syndrome. By contrast, serotonin antagonists are of little value and the efficacy of interferon therapy has yet to be established.