Carcinoid apudomas

Since the original description of gross and microscopic features of carcinoid tumor almost a century ago, these tumors have fascinated medical professionals because of their rarity, relatively slow growth and association with a clinically dramatic symptom complex. Even though a unitarian hypothesis to explain histogenesis of variegated carcinoids such as those arising from the bronchus and rectum has been proposed and is increasingly accepted, the clinical behavior of carcinoid tumors may vary depending upon location. Appendiceal carcinoids rarely metastasize and hence do not constitute a systemic problem. Extra-appending carcinoid tumors may metastasize, producing a devastating symptom complex. Rectal carcinoid tumors, by contrast, can metastasize but rarely produce the carcinoid syndrome. The relatively uncommon ovarian carcinoids may produce carcinoid syndrome even without hepatic metastases because carcinoid secretions reach the systemic circulation, bypassing the portal venous system and thus escaping hepatic catabolism of these bioactive substances. Treatment of carcinoid tumors remains primarily surgical. Resection of primary tumor should be done even in the presence of metastases to reduce the bulk of functionally active tumor tissue, although the extent of resection depends upon location, size, histologic evidence of invasion and known metastatic propensity of the carcinoid tumor in that location. Hepatic metastases should be treated by resection whenever technically feasible and by hepatic dearterialization with or without chemotherapy. Regional or systemic manifestations of carcinoid syndrome may be relieved by various antiserotonin and antibradykinin agents, although therapeutic relief is not always assured — and, if achieved, is transient. The histogenesis of the carcinoid tumor and the relation of carcinoid tumors to other endocrine and nonendocrine tumors producing “ectopic” hormones is discussed in detail. Although the hypotheses presented are by no means universally accepted, they are a fascinating entree to an understanding of the pathophysiology of this disease. The rarity of the disease and thus the paucity of clinical material needed to develop firm guidelines in the diagnosis and management of carcinoid tumors, however, is compensated for by the intensive study of each patient with this disease and the extensive interest carcinoid tumors and carcinoid syndrome have generated over the past few decades.