Radiation-Associated Low-Grade Extraskeletal Osteosarcoma of the Neck Following Treatment for Thyroid Cancer.

Low-grade extraskeletal osteosarcoma is a rare tumor that may arise de novo or following radiation therapy. Because of the low-grade histology, it may be misdiagnosed as a benign lesion. We present a case of a 59-year-old man with a past history of radiotherapy for papillary carcinoma of the thyroid, presenting 16 years later with a low-grade extraskeletal osteosarcoma of the neck. The patient was treated with surgical excision and is disease free after 12 months of follow-up. The prognosis for patients with low-grade extraskeletal osteosarcoma is relatively good when compared with high-grade sarcomas. While there is a report of a low-grade extraskeletal osteosarcoma arising following radiotherapy for a benign condition, to the best of our knowledge this is the first reported case of a low-grade extraskeletal osteosarcoma occurring following radiotherapy for thyroid cancer, and the only case reported in the soft tissue of the head and neck region.