Poorly differentiated carcinoma of the lung

Poorly differentiated carcinoma of the lung, also poorly differentiated lung carcinoma, is an unclassified lung tumour with features of small cell carcinoma and non-small cell lung carcinoma.

Categorically, it is grouped with non-small cell lung cancer.

General

• Should be used when the DDx is small cell carcinoma versus non-small cell carcinoma.
• Poorly differentiated carcinoma leaves the surgical options on the table.

Microscopic

Features:

• Small cell carcinoma/basaloid squamous cell carcinoma-like tumour.

DDx:

• Lung metastasis - history and imaging important.
• Small cell carcinoma of the lung.
• Squamous cell carcinoma of the lung.

IHC

• Lack of staining with neuroendocrine markers (chromogranin A -ve, synaptophysin -ve, CD56 -ve).
• Keratins +ve.

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Lung, Left Lower Lobe, Core Biopsy: 
- POORLY DIFFERENTIATED CARCINOMA, see comment. 

COMMENT: 
The tumour stains as follows: 
POSITIVE: EMA, AE1/AE3. 
NEGATIVE: TTF-1, chromogranin A, synaptophysin, CD56, CD45, CK5/6, p63.

The morphology would be compatible with small cell carcinoma or basaloid 
squamous cell carcinoma.  

The neuroendocrine markers (chromogranin A, synaptophysin, CD56) and the squamoid 
markers available (p63, CK5/6) are negative; thus, the tumour is not further classified. 

See also

• Lung tumours.
• Non-small cell lung carcinoma.