TTF-1 and Napsin A double stain: a useful marker for diagnosing lung adenocarcinoma on fine-needle aspiration cell blocks.

BACKGROUND: Immunohistochemistry (IHC) for thyroid transcription factor-1 (TTF-1) is used to confirm the diagnosis of lung adenocarcinoma. Napsin A also has shown positivity in lung adenocarcinoma. A combined double stain for TTF-1 and napsin A has been proposed to achieve higher sensitivity and specificity. In this study, the authors evaluated the utility of this double stain in the diagnosis of lung adenocarcinoma in cell blocks of fine-needle aspirates (FNA).

METHODS: The authors used a cohort comprising 35 FNA cell blocks of lung adenocarcinoma and 24 FNA cell blocks of lung squamous cell carcinoma (SqCCA). IHC was performed; expressions of TTF-1 as brown nuclear stain and of napsin A as red cytoplasmic stain were identified.

RESULTS: Twenty-six of 35 (74%) lung adenocarcinomas were positive for double staining with TTF-1/napsin A. Of 35 lung adenocarcinomas, only 2 (5%) were positive for TTF-1 alone and 3 (8%) were positive for napsin A alone. For the double stain TTF-1/napsin A, 3 of 24 (12%) lung SqCCAs were positive for both. Six of 24 (25%) cases were positive for TTF-1 alone, and none were positive for napsin A alone. For lung adenocarcinoma, TTF-1/napsin A has a sensitivity of 74%, specificity of 87%, accuracy of 79%, and a positive predictive value of 89%.

CONCLUSIONS: The double IHC stain, TTF-1/napsin A, for the identification of pulmonary adenocarcinoma in FNA cell block materials was diagnostically useful. The use of napsin A alone demonstrated a greater degree of accuracy and appeared diagnostically useful as a single IHC stain.