An analysis of rare carcinoid tumors: clarifying these clinical conundrums.

Carcinoid tumors are distinct neuroendocrine neoplasms with characteristic histological, clinical, and biological properties. Though commonly associated with the gastrointestinal tract and bronchopulmonary system, a substantial number of these tumors originate in less common anatomical sites and can range from indolent, unrecognized entities to highly active, metastatic secretory tumors. Their presentation within unfamiliar locations often results in clinical confusion, and they persist as unrecognized lesions, subjecting patients to delayed, inappropriate, or ineffective treatment. The authors reviewed 13,715 carcinoid tumors identified by three consecutive registries of the National Cancer Institute (NCI) from 1950 to 1999, focusing on the anatomic sites accounting for less than one percent of all carcinoids. In addition, data from the world's literature published on carcinoid tumors within these particular anatomic locations were then analyzed with respect to incidence, clinical presentation, symptoms, diagnostic evaluation, microscopic and immunohistochemical findings, treatment strategies, and prognosis. The primary organs in which carcinoids are most commonly mistaken for some of the more conspicuous endemic tumors include the esophagus, pancreas, liver, biliary tract, gallbladder, and Meckel's diverticulum, as well as within the pelvic and otolaryngeal organs and the breast. In general, the highest proportion of "rare" carcinoids was identified in the gastrointestinal (GI) tract, with the ovary as the single most affected extra-GI site. Tumors with the worst prognosis were those that involved the pancreas (37.5%: 5-year survival) and those in the cervix (12-33%: 3-year survival). While gastrointestinal carcinoids have become a more recognized entity and thus more amenable to identification, similar lesions are often not considered in other sites and have often either been overlooked or misdiagnosed. Widespread reports of their occurrence in rare locations warrants attention. The diminution of the likelihood of inadvertently neglecting these often benign, indolent neoplasms that are well known to metastasize if unaddressed would represent an important advance. Familiarity with such unusual sites of origin will facilitate appropriate recognition and characterization of such tumors, allowing for timely intervention.