Squamous cell carcinoma

It accounts for about one-third of all primary lung malignancy. Most of these tumors arise in a central location, the remainder in smaller bronchi.

Rare variants:

  • papillary
  • clear cell
  • small cell
  • basaloid

Cytologic diagnostic features (well-differentiated tumors)

  • Abundant dyshesive cells, that may be polygonal, rounded or elongated
  • Dense cytoplasmic orangeophilia (Papanicolaou stains)
  • Pleomorphic, hyperchromatic and often pyknotic nuclei
  • Obscured nucleoli and chromatin detail
  • Tadpole or fiber-like cells
  • Frequent anucleate cells
  • Twisted keratin strands (Herxheimer spirals)

Tadpole or fiber-like cells are bizarre, elongated, spindle-shaped cells which can often be seen. An abundant granular debris, necrosis and inflammation are common.

The cells of moderately or poorly differentiated tumors show larger nuclei with coarse and granular chromatin texture and cyanophilic cytoplasm (with Papanicolaou stains); they are often arranged in thick groups. Keratinization is rare or absent. In poorly-differentiated tumors a definitive diagnosis of squamous cell carcinoma can be sometimes hard to be made; a diagnosis of non-small cell carcinoma should be made in these cases.

False-positive diagnosis may occur as a result of overinterpretation of reparative or metaplastic changes. False-negative diagnoses may occur when only necrotic and inflammatory material is obtained.

Differential diagnosis

  • Repair
  • Squamous metaplasia
  • Degeneration
  • Mesothelial cells
  • Radiation/chemoterapy effect
  • Upper airway cancer contamination


  • Cytokeratin 7 –
  • Cytokeratin 5 +
  • Cytokeratin 20 –
  • Neuroendocrine markers –
  • TTF-1 –

Squamous cell carcinoma:

Squamous cell carcinoma. Numerous keratinized (orangeophilic) and non-keratinized malignant squamous cells dispersed in a background of keratinaceous debris (FNAB).
Squamous cell carcinoma. Malignant keratinized squamous cells with marked pleomorphism and keratinaceous debris.  
Squamous cell carcinoma. Malignant heavily keratinized squamous cells (appearing orangeophilic) with marked pleomorphism in a background of necrotic cytoplasmic fragments.  
Squamous cell carcinoma. Note the extensive tissue necrosis, keratinaceous debris, and a single viable malignant keratinized cell (at 2 o' clock).
Squamous cell carcinoma. An elongated "tadpole-shaped" malignant keratinized cell with heavily keratinized (orangeophilic) cytoplasm.

Occult carcinoma in situ:

Occult carcinoma in situ
Occult carcinoma in situ
Occult carcinoma in situ
Occult carcinoma in situ


FNA moderately differ
FNA well differ
FNA well differ
FNA well differ
Transbronchial FNA

Bronchial brush:

Bronchial brush
Bronchial brush
Bronchial brush