Thyroid transcription factor 1 and napsin a double staining in lung adenocarcinoma in pleural fluid.

OBJECTIVE: Thyroid transcription factor 1 (TTF-1)/napsin A double staining is useful for the identification of primary lung adenocarcinoma. We examined its performance in pleural fluid.

STUDY DESIGN: Thirty-eight pleural-fluid specimens with lung adenocarcinoma were identified. Among these, 23 cases were diagnosed with a lung primary adenocarcinoma and 15 with a nonlung primary adenocarcinoma [breast (n = 13), ovarian (n = 1) and esophageal (n = 1)]. Immunohistochemistry was performed on formalin-fixed, paraffin-embedded cell blocks. Expression of TTF-1 as a brown nuclear stain and napsin A as a red cytoplasmic stain were identified as positive staining.

RESULTS: In lung adenocarcinoma, 19 out of the 23 (83%) cases were positive for the TTF-1/napsin A double stain, 1 (4%) was positive for TTF-1 only, 2 (9%) were positive for napsin A only and 1 (4%) was negative for the TTF-1/napsin A double stain. All 15 cases of nonlung primary adenocarcinoma were negative for the TTF-1/napsin A double stain.

CONCLUSION: The sensitivity of napsin A for diagnosing lung adenocarcinoma is slightly higher than that of TTF-1.