Algorithm of Rekhtman et al for Using Immunostains to Classify a Non-Small Cell Lung Carcinoma (NSCLC)

 

Patient selection: non-small cell lung carcinoma

 

Iniital Panel of immunostains:

(1) TTF-1 (a positive result with a specific clone indicates adenocarcinoma)

(2) p63 (a positive result usually indicates a squamous cell carcinoma)

 

Immunostains	TTF-1 >= 50% reactive	TTF-1 > 0% and < 50% positive	TTF-1 negative
p63 >= 50% positive	adenocarcinoma (see below)	squamous cell	squamous cell
p63 >0% and < 50% positive	adenocarcinoma	adenocarcinoma	indeterminate
p63 negative	adenocarcinoma	adenocarcinoma	indeterminate, favor adenocarcincoma

 

For the indeterminate result of TTF-1 negative and p63 >0% and < 49%, a positive immunostain for CK5/6 indicates squamous cell carcinoma.

 

For the TTF-1 > 0% and < 49% and p63 > 0% and < 49% (center aquare) an adenocarcinoma should show TTF-1 stronger than p63 (high TTF-1 to p63 ratio).

 

Approximately 90% of adenocarcinomas are TTF-1 positive (> 0%). Weak TTF-1 staining can be seen in squamous cell carcinoma if an immunostain from a less specific clone is used. A positive immunostain for Napsin A will confirm the adenocarcinoma.

 

A small percent of tumors will show both adenocarcinoma and squamous cell carcinoma differentiation. These should be TTF-1 and p63 positive, and additional immunostains should support the dual differentiation.