This antibody labels the Thyroid Transcription Factor-1 (TTF-1) protein in the nucleus of follicular epithelial cells in normal thyroid and thyroid tumors, in nuclei of type II pneumocytes, Clara cells, and basal cells of terminal bronchioles in normal lung and lung adenocarcinomas. It is a useful tool for differentiating primary versus metastatic tumors in lung and thyroid when used in a panel of antibodies.