Adenocarcinomas are the most common epithelial malignancies in body cavity fluids. Subclassification of adenocarcinomas according to primary site can be a challenging task. Thyroid transcription factor 1 (TTF-1) is a nuclear transcription factor that is expressed in normal lung, in thyroid, and in their neoplasms. Because thyroid carcinomas rarely metastasize to the serosal surfaces, the authors used TTF-1 as a marker to distinguish adenocarcinomas of the lung from carcinomas of other organs.
The authors studied 113 body cavity fluids (92 pleural fluid samples and 21 ascitic samples) from 113 patients with a diagnosis of adenocarcinoma on the basis of routine cytology. The primary sites of origin were confirmed clinically or histologically for all patients. There were 39 adenocarcinomas of the lung, 24 adenocarcinomas of the breast, 34 adenocarcinomas of the genitourinary tract, and 16 adenocarcinomas of the gastrointestinal tract. Archival Papanicolaou-stained, cytocentrifuged slides were used without destaining for immunocytochemistry with the monoclonal TTF-1 antibody using a commercial available method.
TTF-1 was expressed in 21 of 39 lung adenocarcinomas (54%). Intense nuclear staining was present in tumor cells that occurred in groups or in isolated form. In contrast, none of the other types of adenocarcinomas expressed TTF-1.
TTF-1 is a highly specific marker for adenocarcinomas of the lung in body cavity fluids. Immunocytochemistry using this antibody can be performed easily on archival Papanicolaou-stained, cytocentrifuged slides of fluid specimens.