Thyroid transcription factor-1 is highly sensitive and specific in differentiating metastatic pulmonary from extrapulmonary adenocarcinoma in effusion fluid cytology specimens.

Background: Thyroid transcription factor-1 (TTF-1) is a homeodomain-containing transcription factor selectively expressed in thyroid, lung and diencephalon. It has been shown to label pulmonary adenocarcinoma, thyroid tumors, and small cell carcinoma (pulmonary and extrapulmonary) with relatively high sensitivity and specificity. The usefulness of this immunostain in cytology specimens has not been thoroughly discussed in the literature.