Cytology applications of p63 and TTF-1 immunostaining in differential diagnosis of lung cancers

The pathologic distinction of small cell from non-small cell-lung carcinoma is of considerable therapeutic significance. In particular, the ability to distinguish poorly differentiated non-small-cell lung cancer from small-cell lung carcinoma (SCLC) is at times difficult based upon morphology alone; available immunohistochemical markers such as neuroendocrine markers are of limited utility. We have demonstrated the role of p63 and thyroid transcription factor-1 (TTF-1) in the differential diagnosis of poorly differentiated squamous-cell carcinoma (PDSCC) versus SCLC, mostly in biopsy samples (Wu et al., American Journal of Clinical Pathology 2003;119:696-702). Here, we examine further the utility of this panel in cytologic cell-block samples of lung cancers including both primary and metastatic cancers of pulmonary origin, and cases of nonpulmonary cancers metastatic to lung in which differential diagnoses included a lung primary. Four-micron thick sections of 30 alcohol-fixed paraffin-embedded cell blocks from 14 lung FNAs, 6 liver FNAs, 3 bronchial washings, 1 subcarinal lymph node FNA, 1 iliac lymph node FNA, 1 pelvic mass FNA, 1 neck lymph node FNA, 1 adrenal FNA, and 1 pleural effusion were deparaffinized and stained with monoclonal antibodies reactive to p63 (1:800, Santa Cruz Biotechnology) and TTF-1 (1:50, Dako). Slides were stained for p63 using a streptavidin-biotin kit (BioGenex) and diaminobenzidine as chromagen, and counterstained with hematoxylin. Slides were stained for TTF-1 using a Dako Autostainer. Thirty cases were examined, including 8 primary SCLCs, 8 extra-pulmonary metastases of lung SCLCs, 4 PDSCCs and 4 primary pulmonary adenocarcinomas, and 6 nonpulmonary adenocarcinomas metastatic to lung or other sites. Fifteen out of 16 (94%) SCLC cases were p63-/TTF-1+, ranging in intensity from focal-weak to diffuse-strong; 1116 SCLCs from a bronchial washing was p63-/TTF-1- but synaptophysin was positive. All 4 primary lung adenocarcinoma cases were p63-/TTF-1+; contrasting with nonpulmonary adenocarcinomas that were all p63-/TTF-1-. All 4 PDSCC cases were p63+/TTF-1-. The panel of p63 and TTF-1 appears to be useful in the diagnostic evaluation of cytologic cell-block samples of pulmonary malignancy.