Cytomorphologic overlap of differentiated thyroid carcinoma and lung adenocarcinoma and diagnostic value of TTF-1 and TGB on cytologic material.

Thyroid carcinomas and lung adenocarcinoma share cytomorphological features yet have different prognoses. Thyroid Transcription Factor-1 (TTF-1) is an immunohistochemical (IHC) marker used to confirm pulmonary and thyroid carcinoma, while Thyroglobulin (TGB) is expressed by thyroid carcinoma. The cytopathology archive of The Johns Hopkins Hospital was searched for cases of lung adenocarcinoma versus thyroid carcinoma with TTF-1 and TGB IHC. Forty-four cases of lung adenocarcinoma (25) and thyroid carcinoma (19) were retrieved. One was metastatic lung adenocarcinoma to the thyroid and three were metastatic papillary thyroid carcinoma (PTC) to the lung. The initial interpretation of two cases from bony lesions was metastatic lung adenocarcinoma. In light of additional clinical information and TGB immunostain, the diagnoses of these two cases changed to metastatic thyroid carcinoma. TTF-1 and TGB is a small immunostain panel that can differentiate lung adenocarcinoma from thyroid carcinoma and prevent misdiagnosis and its consequences.