hematoxylin and eosin (H&E, A) and immunohistochemistry for thyroglobulin (TG, B), napsin-A (C), TTF-1 (D), and PAX8 (E, Case #12). The metastatic pulmonary adenocarcinoma is positive for napsin-A and TTF-1, whereas negative for TG and PAX8. The background thyroid gland is positive for PAX8, TTF-1, and TG, and is negative for napsin-A.