The value of thyroid transcription factor-1 in cytologic preparations as amarker for metastatic adenocarcinoma of lung origin

In tissue sections, thyroid transcription factor-1 (TTF-1) is a sensitive m arker for adenocarcinomas of lung and thyroid origin. This immunohistochemi cal study evaluates the effectiveness of TTF-1 as a marker for pulmonary ad enocarcinomas in paraffin sections of cell block preparations derived from effusion and fine-needle aspiration specimens. We evaluated 122 cell blocks including 8 primary and 39 metastatic pulmonary adenocarcinomas, 11 pulmon ary neoplasms of other types, 50 specimens with nonpulmonary metastatic tum ors, and 14 mesotheliomas. TTF-1 was reactive in 42 (89%) of 47pulmonary ad enocarcinomas. Only 1 of 4 pulmonary small cell/neuroendocrine tumors was T TF-1 positive, while I of 7 squamous cell carcinomas was weakly reactive. O f 50 metastatic tumors of nonpulmonary origin, focal weak reactivity was no ted only for 1 metastatic ovarian carcinoma. All mesotheliomas were nonreac tive. In cytologic preparations, TTF-1 is a highly selective marker for pul monary adenocarcinoma and also can have a role in the distinction between p ulmonary adenocarcinoma and mesothelioma.