Thyroid transcription factor-1 and cytokeratins 7 and 20 in pulmonary and breast carcinoma

OBJECTIVE: To evaluate the immunohistochemical expression of a lung epithelial gene transcription factor, thyroid transcription factor-1 (TTF-1), in lung anti breast carcinoma in pulmonary cytologic preparations and to correlate the results with the expression of cytokeratin 7 (CK7) and 20 (CK20). STUDY DESIGN: Cell blocks of cytologic specimens were immunostained with antibodies to TTF-1, CK7 and CK 20. Specimens included 41 primary lung carcinomas (21 adenocarcinomas, 8 squamous cell carcinomas and 12 small cell undifferentiated carcinomas) and 6 metastic breast adenocarcinomas. RESULTS: The lung adenocarcinomas showed nuclear reactivity for TTF-1 in 76% (16/21) of the cases and a staining combination of CK7+/CK20- in 95% (20/21) of the cases. Only one case was CK7+/CK20+. All the breast carcinomas were nonreactive to TTF-1, and all were CK7+/CK20-. The squamous cell carcinomas and small cell undifferentiated carcinomas showed TTF-1 positivity in 38% (3/8) and 83% (10/22), respectively. CONCLUSION: Immunostaining for TTF-1 distinguishes lung adenocarcinomas from breast adenocarcinomas in cytologic specimens, whereas the combination of CK7 and CK20 immunostaining does not make that distinction. TTF-1 is sensitive and highly specific to primary lung adenocarcinoma, and its nuclear staining localization facilitates interpretation.