Karzinoide

Karzinoide, also known as carcinoid tumors, are a subset of neuroendocrine tumors that originate from neuroendocrine cells, most often enterochromaffin cells in the gastrointestinal tract or in the lungs. Most karzinoide tumors are slow-growing and can be either functional, secreting hormones such as serotonin, or nonfunctional.

Common sites include the appendix, small intestine (jejunum and ileum), and rectum, with other gastrointestinal sites and the lungs also affected. Behavior ranges from indolent to more aggressive; well-differentiated tumors have lower proliferation indices than poorly differentiated neuroendocrine carcinomas.

Clinical features depend on secretion. Functional tumors may cause carcinoid syndrome, characterized by flushing, diarrhea, abdominal cramps, wheezing, and, with long-standing disease, carcinoid heart disease affecting the right side of the heart. Carcinoid syndrome is most often seen with liver metastases that allow hormone release into the systemic circulation; primary pulmonary carcinoids can cause symptoms even without liver metastases.

Diagnosis is based on histology showing neuroendocrine differentiation (markers such as chromogranin A and synaptophysin) and radiologic or imaging studies. Biochemical tests include 24-hour urinary excretion of 5-HIAA and plasma chromogranin A. Functional imaging with Octreoscan or Ga-68 DOTATATE PET/CT helps determine receptor expression and staging.

Treatment depends on stage and grade. Localized disease is usually managed by surgical resection. In advanced disease, somatostatin analogs (octreotide, lanreotide) control symptoms and may slow progression. Additional options include peptide receptor radionuclide therapy (PRRT), targeted therapies (everolimus, sunitinib in selected neuroendocrine tumors), and cytotoxic chemotherapy for high-grade carcinomas. Liver-directed therapies and multidisciplinary care are common.

Prognosis varies by site and grade; appendiceal carcinoids often have excellent outcomes, while midgut and pancreatic neuroendocrine tumors carry greater risk.