Bronchial Carcinoid and Neuroendocrine Lung Tumours
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Direct answer
Bronchial carcinoid is a low-grade neuroendocrine tumour of the bronchial tree, classed as typical or atypical, on a spectrum ending in high-grade neuroendocrine carcinomas. Typical carcinoids are central, slow-growing and usually cured by surgical resection, whereas atypical carcinoids grow faster, spread to nodes more often and are linked with smoking. Central tumours tend to cause obstruction, haemoptysis or recurrent pneumonia, and carcinoid syndrome is uncommon.
What you must remember
- Typical carcinoid: fewer than two mitoses per 2 mm² and no necrosis, usually a central endobronchial lesion.
- Atypical carcinoid: two to ten mitoses per 2 mm² and/or necrosis, more often peripheral, with greater nodal spread.
- Presentation: cough, haemoptysis, wheeze and post-obstructive pneumonia, and a central tumour is often mistaken for asthma.
- Carcinoid syndrome: flushing, diarrhoea and bronchospasm, usually from hepatic metastases releasing serotonin rather than from the bronchial primary.
- Ectopic hormones: atypical carcinoid can secrete ACTH, causing Cushing syndrome.
- Staging imaging: somatostatin receptor scintigraphy, the octreotide scan, or a somatostatin analogue PET tracer localises receptor-positive tumours.
- Treatment: surgical resection, often lobectomy or sleeve resection, is usually curative for localised typical carcinoid.
Typical, atypical and high-grade neuroendocrine tumours compared
Lung neuroendocrine tumours form a spectrum, and grading by mitoses and necrosis decides both treatment and prognosis. The comparison below separates the three main entities commonly examined, and each row carries a different management pathway that examiners expect students to recall without hesitation.
| Feature | Typical carcinoid | Atypical carcinoid | Small cell carcinoma |
|---|---|---|---|
| Mitoses per 2 mm² | Fewer than 2 | 2 to 10 | Very high |
| Necrosis | Absent | Present in some | Extensive |
| Typical site | Central | Central or peripheral | Central |
| Smoking link | Weak | Strong | Strong |
| Behaviour | Slow, rarely metastasises | Intermediate, nodal spread | Rapid, early metastasis |
| Usual treatment | Surgical resection | Surgery with nodal sampling | Platinum chemotherapy and radiotherapy |
Borderline mitotic counts are common on small biopsies, so the pathologist should report the mitotic count per 2 mm² together with the necrosis status and the Ki-67 index, and the clinician should ask for review when the grade is borderline.
Grade follows the mitotic count and necrosis, with Ki-67 used as supporting evidence. The distinction matters because the treatment and prognosis differ sharply between the rows, and a wrong grade leads either to needless chemotherapy or to under-treatment of a tumour that needs more aggressive surveillance.
Where the exam tries to catch you
Central carcinoids masquerade as common chest problems, and the grading question is often the one that is missed.
- Trap: treating a central carcinoid as asthma or pneumonia Correct: recurrent collapse or pneumonia in one lobe needs bronchoscopy to look for an endobronchial lesion.
- Trap: assuming all lung neuroendocrine tumours are chemosensitive small cell carcinoma Correct: typical carcinoids are managed mainly by surgery, and chemotherapy is reserved for high-grade disease.
- Trap: attributing carcinoid syndrome to a bronchial primary Correct: flushing and diarrhoea usually reflect hepatic metastases releasing serotonin, not the bronchial tumour alone.
- Trap: expecting octreotide to treat the primary tumour Correct: octreotide scanning localises receptor-positive tumours and controls hormonal symptoms, but does not cure them.
Frequently asked questions
What distinguishes typical from atypical bronchial carcinoid?
Typical carcinoid has fewer than two mitoses per 2 mm² and no necrosis, whereas atypical carcinoid has two to ten mitoses per 2 mm² and may show necrosis. Atypical tumours are more aggressive and more likely to involve lymph nodes.
Why does carcinoid syndrome usually need liver metastases?
Carcinoid syndrome usually requires hepatic metastases, because the liver is the site where tumour-secreted serotonin escapes first-pass metabolism. A bronchial carcinoid without metastases rarely produces flushing or diarrhoea.
Which scan localises somatostatin receptor-positive lung neuroendocrine tumours?
Somatostatin receptor scintigraphy, the octreotide scan, localises somatostatin receptor-positive lung neuroendocrine tumours throughout the body. Newer somatostatin analogue PET tracers are also used in many centres for staging, and they are preferred where available.
Is small cell carcinoma a neuroendocrine tumour of the lung?
Small cell carcinoma is a high-grade neuroendocrine carcinoma of the lung, distinct from typical and atypical carcinoids. It is aggressive, usually central, and is treated with platinum-based chemotherapy with radiotherapy.
Which treatment is usually curative for a localised typical carcinoid?
Surgical resection, typically lobectomy or sleeve resection, is usually curative for a localised typical bronchial carcinoid. Lymph node assessment is part of the operation, and surgery remains the mainstay of treatment.