Thyroid Metastasis of the Osteosarcoma: Management of the Third Reported Case with a Multidisciplinary Approach

Osteosarcoma commonly metastasizes to the lungs, while thyroid involvement is extremely rare due to the gland's high vascularity. This report presents the third known case of osteosarcoma metastasis to the thyroid, underscoring the importance of thyroid evaluation and multidisciplinary management.

A 34-year-old woman with a history of right distal femoral osteosarcoma treated with wide resection and tumor prosthesis reconstruction presented six years later with a progressively enlarging thyroid mass. FDG PET/CT showed a hypermetabolic lesion in the left thyroid lobe (SUV max 12.7). Fine-needle aspiration biopsy followed by histopathological and immunohistochemical analysis confirmed metastatic osteosarcoma. Immunohistochemistry was negative for thyroglobulin, PAX-8, and TTF-1, and positive for vimentin. The patient underwent total thyroidectomy.

Although exceedingly rare, thyroid metastasis should be considered in osteosarcoma patients presenting with thyroid lesions. In our case, thyroid involvement occurred as a late-onset metastasis several years after the initial diagnosis, emphasizing the need for vigilance during long-term follow-up. This case highlights the value of early recognition and multidisciplinary care, contributing to the limited literature on the atypical metastatic behavior of osteosarcoma.