TTF1 and medullary thyroid gland carcinoma: Neoplastic cells showed strong immunoreactivity to chromogranin A and synaptophysin, but the immunohistochemical profile was inconsistent with medullary thyroid carcinoma in that the tumor was negative for calcitonin, carcinoembryonic antigen (CEA), and thyroid transcription factor-1 (TTF-1) (Figure 1).