MON-454 Lower Extremity Leiomyosarcoma Metastatic to a Benign Thyroid Nodule

Background: Metastases to the thyroid gland from non-thyroidal malignancies have been reported in 1.4-3% of patients undergoing thyroid surgery for malignant thyroid tumors, but only 4% of these are due to sarcomas(1). Metastases in a pre-existing thyroid nodule are even more rare. We present a patient with a lower extremity leiomyosarcoma that metastasized to a pre-existing benign thyroid nodule. Clinical Case: A 70-year-old woman was referred to the Thyroid Nodule Clinic for a 5 cm thyroid nodule replacing most of the right thyroid lobe. Twenty years earlier the patient had a left thyroid lobectomy for a benign nodule. One year before presentation, she was diagnosed with a high grade lower extremity leiomyosarcoma with lung metastases and started on treatment. A large right thyroid nodule pressing on the trachea was incidentally found on an initial chest CT performed for sarcoma staging. On PET-CT, the nodule was not FDG-avid. On ultrasound, the thyroid nodule was solid and heterogeneous, iso- to hyperechoic with smooth margins, inspissated colloid and grade 3 vascularity. Fine needle aspiration (FNA) of the nodule showed benign cytology (Bethesda II). The patient did not have local compressive symptoms and decided not to undergo surgical removal of the nodule. The thyroid nodule was initially stable on periodic follow-up CT scans and thyroid ultrasounds. However, a thyroid ultrasound performed 2.5 years later showed a change in the nodule echogenicity without change in size. The nodule had become hypoechoic, heterogeneous and well-defined with grade 2 vascularity. FNA revealed a poorly differentiated malignant spindle cell neoplasm, similar to biopsies of other metastatic sites, supporting a diagnosis of metastatic high grade sarcoma. The patient underwent a right thyroidectomy; pathology revealed a 4.1 cm metastatic sarcoma with multifocal angioinvasion with tumor present at the surgical margin. Follow-up neck ultrasounds showed no evidence of local recurrence, while the patient was receiving chemotherapy for pulmonary metastases. The patient died 3 years later due to a massive pulmonary embolism. Conclusion: To our knowledge, this is the first report of a lower extremity leiomyosarcoma metastatic to a benign thyroid nodule. Although metastasis of an extra-thyroidal malignancy to a pre-existing benign thyroid nodule is very rare, patients with thyroid nodules and a history of malignancy should have regular surveillance of the nodule by ultrasound, and any changes in the nodule features concerning for malignancy should be evaluated with FNA of the nodule. 1. Chung, A. Y., Tran, T. B., Brumund, K. T., Weisman, R. A., & Bouvet, M. (2012). Metastases to the thyroid: a review of the literature from the last decade. Thyroid, 22(3), 258-268.