Objective 1) Understand the presentation and diagnostic workup for malignant fibrous histiocytoma metastatic to the thyroid gland. 2) Be able to discuss different treatment strategies for malignant fibrous histiocytoma metastatic to the thyroid. Methods: Case Report Results: Our patient with al left thyroid mass removed with thyroid lobectomy yielded a 200 gram left lobe measuring 9.5 × 7.5 × 5.4 centimeters. Histopathologic analysis revealed a cellular malignant neoplasm composed of spindle cells in a fascicular arrangement, suggestive of high grade metastatic sarcoma. Immunohistochemistry differentiated this lesion from anaplastic thyroid carcinoma and supported a diagnosis of malignant fibrous histiocytoma metastatic to the thyroid. Despite these findings, the patient elected not to proceed with a completion thyroidectomy. Conclusions: Malignant fibrous histiocytoma metastatic to the thyroid is a rare clinical entity, with only five cases reported in the literature. However, it merits consideration in the differential diagnosis of patients presenting with rapidly enlarging thyroid masses, especially those with a history of primary malignant fibrous histiocytoma elsewhere in the body. The foundation of treatment is wide local excision with adjuvant radiation and/or chemotherapy utilized on a case by case basis.
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