Immunostaining for thyroid transcription factor-1 on fine-needle aspiration specimens of lung tumors: a comparison of direct smears and cell block preparations.

Abstract

Fine-needle aspiration (FNA) is used commonly for the diagnosis of pulmonary neoplasms. It has been reported that thyroid transcription factor-1 (TTF-1) is a sensitive and specific marker for certain primary lung tumors. To the authors' knowledge, the use of TTF-1 immunostaining on FNA smears has not been documented in the literature. This study was designed to examine the utility of TTF-1 immunostaining on FNA specimens from various types of lung tumors by comparing the expression rates on Papanicolaou (Pap)-stained and Diff-Quik (DQ)-stained smears with the expression rates on cell block (CB) sections. Forty-three FNA specimens of lung tumors were studied, including 34 primary tumors (14 adenocarcinomas, 12 squamous carcinomas, and 8 small cell carcinomas) and 9 metastatic tumors. One Pap-stained slide and one DQ-stained slide were selected from each tumor. The cytologic material from the slides was transferred to positively charged slides. Unstained recuts were obtained from the CB sections. All slides were stained with TTF-1 monoclonal antibody using heat-induced epitope retrieval and a labeled polymer detection system. Twelve of 14 pulmonary adenocarcinomas were positive for TTF-1 (11 specimens on both CB sections and Pap-stained smears and 1 specimen on all 3 preparations, including the DQ-stained smear). Two of 14 adenocarcinomas were negative for TTF-1. Of 12 pulmonary squamous carcinomas, only 1 was positive for TTF-1 (on the CB section and the Pap-stained smear); the others were negative in all 3 preparations. Of eight small cell lung carcinomas, six specimens showed positive staining for TTF-1 on both CB and Pap-stained preparations; one of those also was positive on the DQ-stained smear. The remaining two small cell lung carcinomas were negative for TTF-1 in all three preparations. All metastatic tumors were negative for TTF-1. TTF-1 immunostaining of pulmonary neoplasms was applicable to FNA smears that were stained previously with the Pap technique, and the rate of positive staining in each tumor type was identical to the rate of positive staining in CB sections and was comparable to that reported in previous publications. Smears previously stained with the DQ method were unreliable for TTF-1 immunostaining.