Evaluation of napsin A, cytokeratin 5/6, p63, and thyroid transcription factor 1 in adenocarcinoma versus squamous cell carcinoma of the lung.

CONTEXT

The distinction of lung adenocarcinoma from other types of primary lung malignancies is important clinically. Accurate morphologic classification is often hindered because 70% of lung cancers are diagnosed on limited fine-needle aspiration or transbronchial biopsy specimens. Although thyroid transcription factor 1 (TTF-1) has historically been the most specific marker for lung adenocarcinoma, a relatively new marker, napsin A, has recently been shown to be more sensitive and specific than TTF-1.

OBJECTIVE

To find the most cost-effective panel to reliably distinguish lung adenocarcinoma from squamous cell carcinoma.

DESIGN

A total of 291 lung cancers were evaluated morphologically (197 adenocarcinomas [75%]; 66 squamous cell carcinomas [25%]; 28 cases could not be classified into either and were dropped). Immunohistochemistry for napsin A, Cytokeratin 5/6, p63, and TTF-1 was performed on a formalin-fixed tissue microarray obtained from Toyama, Japan. Cases were scored as positive or negative against a negative control.

RESULTS

Napsin A had 83% sensitivity and 98% specificity and TTF-1 had 60% sensitivity and 98% specificity for adenocarcinoma. Cytokeratin 5/6 had 53% sensitivity and 96% specificity and p63 had 95% sensitivity and 86% specificity for squamous cell carcinoma. A panel of napsin A and p63 has a specificity of 94% and a sensitivity of 96% for distinguishing adenocarcinoma from squamous cell carcinoma.

CONCLUSIONS

The source of the antibody is important in avoiding false-negative results. The most cost-effective tissue-preserving panel for small biopsy specimens in the differential diagnosis of lung adenocarcinoma versus squamous cell carcinoma is a combination of p63 and napsin A.