Primary osteosarcoma of the thyroid gland: report of a rare neoplasm Osteossarcoma primário da glândula tireoide: relato de uma neoplasia rara

ABStrACt Primary mesenchymal tumors of the thyroid gland are extremely rare. The authors report a case of primary thyroid osteosarcoma in a male patient presenting a tumoral mass in the neck. CT scan demonstrated a large tumor in the right thyroid lobe with areas of calcification. The surgical specimen consisted of a hard brown-gray tumor, measuring 13 × 11 × 7.5 cm. Microscopy revealed a high-grade malignant neoplasm composed of polygonal cells of intermediate size, chondroid pattern in some areas and osteoid formation. The process was immunonegative for AE1/AE3, glial fibrillary acidic protein (GFAP), epithelial membrane antigen (EMA), p53 and thyroid transcription factor-1 (TTF-1), and immunopositive for CD99 and S100. Thus the diagnosis of primary osteosarcoma of the thyroid gland was established.