Carcinoid tumors are rare, but their incidence has increased over the past few decades due to better detection methods. The estimated annual incidence in the United States is approximately 5 to 7 cases per 100,000 people. They represent about two-thirds of all neuroendocrine tumors.

The exact cause of carcinoid tumors is not fully understood. They are thought to arise from genetic mutations affecting neuroendocrine cells. While most cases are sporadic, some familial syndromes, such as Multiple Endocrine Neoplasia type 1 (MEN1), are associated with an increased risk of developing carcinoid tumors. Risk factors include chronic atrophic gastritis, smoking (for lung carcinoids), and family history of neuroendocrine tumors.

Symptoms vary based on tumor location and whether the tumor secretes hormones:

• Non-functional tumors (most common): Often asymptomatic until large or metastatic; may cause pain, obstruction, or bleeding; often discovered during routine procedures or other surgeries

• Functional tumors: May cause carcinoid syndrome, with:

  • Flushing of the skin

  • Diarrhea

  • Wheezing or asthma-like symptoms

  • Heart valve lesions (especially right-sided)

  • Abdominal cramping

  • Pellegra-like skin lesions due to niacin deficiency (vitamin B3) from serotonin overproduction

Symptoms may worsen after meals, alcohol intake, or stress.

Carcinoid tumors are often discovered incidentally during imaging or surgery for other conditions. Diagnosis is confirmed through a combination of biochemical tests, imaging, and histological analysis.

• 24-hour urinary 5-HIAA (5-hydroxyindoleacetic acid): Elevated in carcinoid syndrome due to serotonin breakdown

• Chromogranin A: A serum marker often elevated in neuroendocrine tumors

• CT or MRI scans: To locate primary and metastatic tumors

• Somatostatin receptor imaging (e.g., Ga-68 DOTATATE PET/CT): Highly sensitive for detecting neuroendocrine tumors

• Endoscopy or colonoscopy: May reveal tumors in the GI tract

• Biopsy: Confirms diagnosis and helps assess tumor grade and differentiation

Treatment depends on the tumor’s location, size, metastatic spread, and functionality:

• Surgery: The primary treatment for localized tumors

• Somatostatin (peptide hormone) analogs (e.g., octreotide, lanreotide): Control symptoms of carcinoid syndrome and slow tumor progression

• Peptide receptor radionuclide therapy (PRRT): Targets somatostatin receptors with radiolabeled compounds (e.g., lutetium-177 DOTATATE)

• Targeted therapy: Agents like everolimus may be used in advanced disease

• Chemotherapy: Reserved for high-grade or rapidly progressing tumors

• Liver-directed therapy: Embolization or ablation for liver metastases

The prognosis for carcinoid tumors varies widely based on tumor grade, stage, and location. Low-grade, localized tumors often have an excellent prognosis, with 5-year survival rates exceeding 90% after surgical removal. However, metastatic disease, particularly involving the liver, lowers survival, although many patients can live for years with stable disease on treatment. Carcinoid heart disease is a serious complication of carcinoid syndrome that can significantly impact outcomes if not managed. Early diagnosis and a multidisciplinary treatment approach can greatly improve quality of life and survival.

1. Carcinoid Tumors - Symptoms and Causes - Mayo Clinic

2. Carbinoid Tumor - Cedars Sinai

3. Johns Hopkins Medicine - Carcinoid Tumor

4. Medline Plus - Carcinoid Tumors