Carcinoids

Carcinoids, commonly referred to as carcinoid tumors, are a subset of neuroendocrine tumors that arise from neuroendocrine cells, most often enterochromaffin cells in the gastrointestinal tract and bronchial epithelium in the lungs. They typically grow slowly and can be either functional, secreting hormones, or nonfunctional.

Most carcinoids are well-differentiated neuroendocrine tumors. Grading relies on the mitotic rate and the Ki-67 index. The majority occur in the small intestine, appendix, colon, rectum, or lungs. A portion may metastasize, frequently to the liver, which can influence symptoms and treatment options.

Clinical presentation varies. Many tumors are asymptomatic and found incidentally. Functional tumors may produce carcinoid syndrome, featuring flushing, diarrhea, wheezing, and, with time, right-sided heart valvular lesions. Carcinoid heart disease is a notable complication of metastatic disease.

Diagnosis combines clinical suspicion with biochemical testing and imaging. Biochemical tests include 24-hour urinary 5-hydroxyindoleacetic acid (5-HIAA) and plasma chromogranin A. Imaging modalities include computed tomography or magnetic resonance imaging, somatostatin receptor imaging (such as octreotide scans) or Ga-68 DOTATATE PET-CT, and histopathology from biopsy confirming neuroendocrine features.

Treatment focuses on disease extent. Localized tumors are usually treated with surgical resection. In advanced cases, somatostatin analogs (octreotide, lanreotide) control hormonal symptoms and may slow progression. Additional options include peptide receptor radionuclide therapy (PRRT) with Lu-177 DOTATATE, liver-directed therapies for liver metastases, and targeted agents like everolimus or sunitinib in selected settings. Chemotherapy is typically reserved for poorly differentiated neuroendocrine carcinomas.

Prognosis is variable, influenced by site, stage, and tumor grade. Carcinoids are rare and often indolent, but outcomes worsen with high-grade or widespread disease. The incidence appears to be rising, partly due to improved detection and testing.