Undifferentiated carcinoma arising from ectopic thyroid tissue in the anterior mediastinum

SummaryA 78-year-old man was admitted with a tumor in the left anterior mediastinum that invaded the trachea and protruded into the lumen. Despite debulking with endobronchial laser followed by a tracheal stent and external radiotherapy, the tumor spread rapidly and extensively. Autopsy findings of the tumor indicated three distinct components: epithelial foci characterized by papillo-tubular structure, sarcoma-like spindle cells, and undifferentiated carcinoma. Immunohistochemical examination revealed that the epithelial foci were positive for thyroglobulin and thyroid transcription factor-1 whereas the spindle cells and undifferentiated carcinoma reacted with antibodies to α-smooth muscle actin and vimentin. Since the tumor was entirely separated from the cervical thyroid, we diagnosed it as undifferentiated carcinoma (spindle cell pattern) arising from ectopic mediastinal thyroid tissue. To our knowledge, this is the first report of undifferentiated carcinoma arising from ectopic thyroid tissue underscoring the need for correct diagnosis and early intervention of the highly malignant disease.