Small cell is central and rapidly metastasising; non-small cell divides into squamous, adeno and large cell
Mnemonic
Divide first into small cell and non-small cell, because it determines treatment:
- Small cell (about 15 per cent) - central, strongly smoking related, arises from neuroendocrine cells, metastasises early, and is rarely operable. Chemosensitive. Causes SIADH and ectopic ACTH, and Lambert-Eaton syndrome
- Non-small cell (about 85 per cent)
- Adenocarcinoma - peripheral, the commonest, and the commonest in non-smokers and in women. Carries the targetable mutations (EGFR, ALK)
- Squamous cell - central, cavitates, strongly smoking related. Causes hypercalcaemia via PTH related peptide
- Large cell - poorly differentiated
“Small cell and squamous are central; adenocarcinoma is peripheral.”
“Squamous secretes PTHrP and calcium; small cell secretes ADH and ACTH” covers the paraneoplastic syndromes most often tested.
A Pancoast tumour at the apex causes Horner’s syndrome, brachial plexus involvement (T1) and rib destruction.
Expansion
| Type | Location | Association | Features |
|---|---|---|---|
| Adenocarcinoma | Peripheral | Commonest overall; non-smokers, women | EGFR, ALK mutations guide targeted therapy |
| Squamous cell | Central | Strong smoking link | Cavitation, hypercalcaemia from PTHrP, keratin pearls |
| Small cell | Central | Almost always smokers | Rapid, early metastasis, paraneoplastic (SIADH, ectopic ACTH, Lambert-Eaton); treated with chemotherapy, not surgery |
| Large cell | Peripheral | Smoking | Poorly differentiated, poor prognosis |
The primary clinical division is small cell versus non-small cell, because it determines treatment: small cell is considered disseminated at diagnosis and treated with chemotherapy and radiotherapy, while non-small cell may be resectable and is increasingly treated by molecular subtype.
Local complications worth grouping: Pancoast tumour at the apex causing Horner syndrome and T1 wasting, recurrent laryngeal nerve palsy causing hoarseness, superior vena cava obstruction, and phrenic nerve palsy.
Squamous cell causes hypercalcaemia and cavitates; small cell causes the endocrine paraneoplastic syndromes. That pairing answers most questions.