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Thyroid transcription factor 1 (TTF-1) plays a key role in morphogenesis of the lungs and is expressed in up to 90% of pulmonary small cell carcinomas.This explains why this marker is frequently used in the search for the primary origin of metastatic endocrine tumours.Here we report on a TTF-1 expressing mixed endocrine-exocrine carcinoma of the common bile duct in a patient with pulmonary nodules that did not appear to be neoplastic.TTF-1 positivity in pulmonary and extrapulmonary neuroendocrine tumours is reviewed,and we conclude that TTF-1 expression in neuroendocrine tumours of the small-cell type are not uncommon at extrapulmonary locations.Therefore,immunohistochem-istry for TTF-1 in such tumours should be interpreted with caution.
Thyroid transcription factor 1 (TTF-1) plays a key role in morphogenesis of the lungs and is expressed in up to 90% of pulmonary small cell carcinomas. This explains why this marker is frequently used in the search for the primary origin of metastatic endocrine tumors. Here we report on a TTF-1 expressing mixed endocrine-exocrine carcinoma of the common bile duct in a patient with pulmonary nodules that did not appear to neoplastic. TTF-1 positivity in pulmonary and extra pulmonary urotension events are reviewed, and we conclude that TTF-1 expression in neuroendocrine tumors of the small-cell type are not uncommon at extrapulmonary locations. Before, immunohistochem-istry for TTF-1 in such tumors should be interpreted with caution.