Expression of thyroid transcription factor-1 in malignant pleural effusions

Separating adenocarcinoma of the lung from nonpulmonary adenocarcinoma or malignant mesothelioma is difficult, especially in cytology specimens. Consequently, it is important to identify markers that may facilitate this distinction. Thyroid transcription factor-1 (TTF-1) is a homeodomain containing transcription factor expressed selectively in the thyroid, lung, and diencephalon. TTF-1 is also expressed in adenocarcinomas of the lung and is widely used as a pulmonary adenocarcinoma marker in surgical specimens. However, the utility of TTF-1 has rarely been investigated in cytology. In this study, we evaluated the expression of TTF-1 in malignant pleural effusions. The primary tumors included 26 pulmonary adenocarcinomas, 26 non-pulmonary adenocarcinomas (13 breast, 5 ovarian, 2 gastric, 2 prostatic, 1 esophageal, 1 colonic, 1 pancreatic and 1 renal) and 4 malignant mesotheliomas. Immunocytochemistry was performed on sections of cell blocks, using a mouse monoclonal TTF-1 antibody (clone 8G7G3/1) and a biotin-streptavidin detection system. Nuclear immunoreactivity for TTF-1 was detected in 19 pulmonary adenocarcinomas. All nonpulmonary adenocarcinomas and malignant mesotheliomas were negative. These data indicate that TTF-1 maintains its sensitivity (73%) and specificity (100%) in cell block preparations and is useful in separating adenocarcinoma of the lung from non-pulmonary adenocarcinoma and malignant mesothelioma in cytology specimens.