[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Lung](https://durgical.com/en/general-pathology/areas/lung/) › Pulmonary neuroendocrine tumours

# 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.

Updated Nov 12, 2026

## Key points

- Typical carcinoid: fewer than 2 mitoses per 10 high-power fields and no necrosis; excellent survival.
- Atypical carcinoid: 2 to 10 mitoses per 10 high-power fields and/or necrosis; more often metastasises.
- High grade: small cell carcinoma and large cell neuroendocrine carcinoma, more than 10 mitoses, extensive necrosis, poor prognosis.
- Central carcinoids: polypoid endobronchial masses covered by intact mucosa, or 'collar-button' lesions through the wall.
- Carcinoid syndrome (flushing, diarrhoea, wheeze) in only a minority of bronchial carcinoids.
- Tumorlets: tiny neuroendocrine nests in scars, of no consequence.

On this page

- The basics Key points
- What it is
- Structure
- Step by step
- The neuroendocrine spectrum of the lung
- Markers
- Memory aid
- Elsewhere in DurgiPedia

- Clinical Clinical notes

- Study Test yourself

- Connections Connections

## 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](https://durgical.com/en/conditions/lung-cancer/) | More than 10 | Extensive | High grade, poor |
| [Small cell carcinoma](https://durgical.com/en/conditions/lung-cancer/) | 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.

## Memory aid

Two and ten divide the carcinoids: under 2 typical, 2 to 10 atypical, over 10 carcinoma.

## 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.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/general-pathology/pulmonary-neuroendocrine-tumours/)

[More Pathology questions →](https://durgical.com/en/practice/?f=pathology)

## Elsewhere in DurgiPedia

- [Pineal gland and the diffuse endocrine system](https://durgical.com/en/histology/pineal-gland-and-the-diffuse-endocrine-system/)

## Connections

## Related 3

- [Immunohistochemistry: the principle and the markers to know](https://durgical.com/en/general-pathology/immunohistochemistry-the-principle-and-the-markers-to-know/)
- [Lung carcinoma: histologic types](https://durgical.com/en/general-pathology/lung-carcinoma-histologic-types/)
- [Gastrointestinal neuroendocrine (carcinoid) tumours](https://durgical.com/en/general-pathology/gastrointestinal-neuroendocrine-tumours/)

## Related conditions 2

- [Lung cancer](https://durgical.com/en/conditions/lung-cancer/)
- [Carcinoid syndrome](https://durgical.com/en/conditions/carcinoid-syndrome/)

[← All of general pathology](https://durgical.com/en/general-pathology/)

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](https://medlineplus.gov/ency/article/000347.htm) (MedlinePlus, US National Library of Medicine, 2025); [Small Cell Lung Cancer](https://www.ncbi.nlm.nih.gov/books/NBK482458/) (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.

---
Source: https://durgical.com/en/general-pathology/pulmonary-neuroendocrine-tumours/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/pulmonary-neuroendocrine-tumours/