Osteosarcoma metastatic to the thyroid gland: A rare case report.

Sarcoma is rarely seen in the thyroid gland and it is difficult to differentiate it from anaplastic thyroid carcinoma. Extraosseus osteosarcoma, a rare malignant nonepithelial neoplasia, can be seen in the thyroid gland, breast, soft tissue, and intraabdominal organs. A 31-year-old woman with a previous history of osteosarcoma of distal femur was presented with a constantly growing mass in her neck accompanied with progressive shortness of breath and worsening dysphagia. On physical examination, a 4 x 5 cm firm mass was palpated in the left lobe of her thyroid gland. Seven years ago, during her pregnancy, she was diagnosed with osteosarcoma of the distal femur and she received chemotherapy and radiotherapy after medical abortion. A year after her initial diagnosis, she underwent surgery for osteosarcoma. Two years later, pulmonary metastasis was detected incidentally in her control computed tomography. She was operated for pulmonary metastasis since there was no remission after chemotherapy. When she presented to the clinic with a neck mass, her thyroid function tests were within the normal range. On computed tomography scan, a 2.5 cm calcified lesion in left lobe of her thyroid gland was detected. Fine-needle aspiration of the thyroid mass displayed numerous discohesive pleomorphic tumors cells identical to osteosarcoma cells seen on her previous knee biopsy specimen. On positron emission tomography, a 3 x 3 x 4.5 cm hypermetabolic lesion with pathologic 18F-FDG uptake on the left side of her neck in thyroid cartilage level was detected. A bilateral total thyroidectomy was performed. The patient was discharged without any complications.