Pulmonary neuroendocrine tumours
- Lesion
Lung neuroendocrine tumours range from harmless tumorlets to low-grade carcinoids to highly aggressive small cell and large cell neuroendocrine carcinomas.
What it is
The bronchial mucosa contains neuroendocrine cells that can proliferate. The spectrum runs from tumorlets and DIPNECH, through carcinoid tumours (low and intermediate grade, often in non-smokers and younger adults), to the high-grade neuroendocrine carcinomas tied to smoking. Carcinoids are separated from carcinomas because their genetics, behaviour and prognosis differ greatly.
Structure
- Gross: spherical, fleshy, well-circumscribed tumour bulging into a bronchus, usually 3 to 4 cm or less.
- Microscopy: organoid nests, trabeculae, ribbons or rosettes of uniform cells with round nuclei and salt-and-pepper chromatin in a delicate vascular stroma.
- Electron microscopy: dense-core neurosecretory granules.
- IHC: chromogranin, synaptophysin, CD56, INSM1; peptides such as serotonin, bombesin and calcitonin.
Step by step
- Neuroendocrine cells of the bronchial mucosa proliferate, sometimes with chronic injury or in DIPNECH.
- Carcinoids have few mutations, often in chromatin regulators (MEN1), unlike smoking-related carcinomas.
- Central tumours grow into the lumen and obstruct the airway.
- Obstruction causes distal atelectasis, pneumonia and bronchiectasis.
- Functioning tumours release serotonin straight into the systemic circulation, so carcinoid syndrome can occur without liver metastases.
The neuroendocrine spectrum of the lung
| Tumour | Mitoses per 10 HPF | Necrosis | Behaviour |
|---|---|---|---|
| Typical carcinoid | Fewer than 2 | None | Low grade, excellent prognosis |
| Atypical carcinoid | 2 to 10 | Focal (punctate) | Intermediate grade |
| Large cell neuroendocrine carcinoma | More than 10 | Extensive | High grade, poor |
| Small cell carcinoma | More than 10 | Extensive | High grade, very poor |
Markers
- Chromogranin
- Synaptophysin
- CD56
- INSM1
Clinical notes
- Persistent cough, hemoptysis, recurrent pneumonia in the same lobe, wheeze in a young adult.
- Resection is usually curative for typical carcinoid; survival is high for typical and lower for atypical carcinoid.
- Carcinoids can also secrete ACTH and cause Cushing syndrome.
Test yourself
Think of the answer, then tap the question to see it.
How are typical and atypical carcinoids distinguished?
By mitotic count and necrosis: typical has fewer than 2 mitoses per 10 high-power fields and no necrosis; atypical has 2 to 10 mitoses and/or necrosis.
What is a collar-button lesion?
A bronchial carcinoid that grows through the bronchial wall and fans out in the peribronchial tissue as well as into the lumen.
Why can a bronchial carcinoid cause carcinoid syndrome without liver metastases?
Its amines are released directly into the systemic circulation, bypassing inactivation in the liver.
Elsewhere in DurgiPedia
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Carcinoid syndrome: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2025); Small Cell Lung Cancer (StatPearls (NCBI Bookshelf), 2025).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.