Diagnosis and therapy of carcinoid tumors—current state of the art and future directions

Carcinoid tumors account for less than 1% of all malignancies and the majority arise in the gastrointestinal system. These tumors are slow growing compared with adenocarcinomas and they differ from the other neuroendocrine malignancies by their protean clinical presentation. Carcinoid tumors were previously considered indolent, but they can manifest malignant characteristics with metastatic spread which often results in a poor prognosis.Although there have been advances in diagnostic and treatment modalities, carcinoid tumors are still often diagnosed late, often when the tumor has metastasized and patients develop carcinoid syndrome. Diagnosis, prognosis and treatment options are based on biochemical markers and imaging investigations. High concentration of urinary 5-HIAA, elevated plasma serotonin and chromogranin A levels help to establish the initial diagnosis of carcinoid tumors. In addition to the CT and MRI, molecular imaging modalities such as OctreoScan, MIBG imaging and more recently PET imaging are vital in detection of primary malignancy and metastatic involvement.Surgery is the mainstay of treatment of nonmetastatic carcinoid tumors. Cytotoxic chemotherapy is not beneficial due to the chemoresistant nature of these tumors. Because carcinoid tumors express somatostatin receptors, somatostatin analogues, which inhibit the release of serotonin and other neuroendocrine peptides, are often used, but their use is limited to symptom control. Treatment using high doses of radionuclides such as radiolabeled somatostatin analogues and MIBG is a more recent option which offers a definite advantage in management. In this article, we review typical features of the carcinoid tumors, examine contemporary methods of detecting and assessing carcinoid tumors and discuss the role of various diagnostic and therapeutic options.