A clinical overview of carcinoid tumors: Perspectives for improvement in treatment using peptide analogs (Review)

Carcinoid tumors were first described more than a century ago, but the treatment of patients with advanced disease remains a challenge to physicians. The etiology of carcinoid tumors, the biologic determinants of the growth of these malignancies, as well as the high frequency of multiple carcinoid and/or non-carcinoid tumors in patients with this disease also remain to be elucidated. A 5-decade analysis of 13,715 carcinoid tumors in the USA showed that distant metastases were demonstrated at the time of diagnosis in 12.9% of patients with this neoplasia. The overall 5-year survival rate for all patients with carcinoids regardless of the site, was reported to be 67.2%. The prognosis of patients with early stage disease is good and surgical resection is the standard form of treatment. The resection of local or regional metastases can result in cure for some cases. However, patients with metastatic dissemination have poor outcomes since chemotherapy is generally ineffective. Surgical resection of isolated hepatic metastases, surgical hepatic artery ligation or embolization produce responses in selected patients. Radiation therapy may ease the pain of bone metastases. The administration of long acting analogs of somatostatin can control the symptoms of diarrhea and flushing in patients with the malignant carcinoid syndrome. However, a complete regression of metastatic carcinoid tumors following the administration of somatostatin analog octreotide has been reported so far in only 3 cases. Other modalities of treatment, including liver transplantation and the administration of radiolabeled somatostatin analogs have likewise been applied in patients with advanced disease. It is expected that advances in proteomics research will contribute to our understanding of the mechanisms of diseases and aid in designing new drugs.