PSUN380 A Case of Sclerosing Epithelioid Fibrosarcoma With Metastases to the Thyroid

BACKGROUND: Sclerosing Epithelioid Fibrosarcoma (SEF) is a rare form of soft tissue sarcoma, often presenting in the soft tissues of the extremities. This tumor is characterized by slow growth, often with local recurrences and/or distant metastases. First described in 1995, subsequent case reports and case series have demonstrated that metastases are primarily to the lung, pleura and bone, but can occur anywhere. Treatment is primarily by wide excision and adjuvant chemotherapy or radiotherapy. However, treatment of this rare form of sarcoma is often unsatisfactory. CLINICAL CASE: A 36-year-old female, had for 30 years presented with a slowly enlarging mass on the left axilla. She had no constitutional symptoms and had previously been in good health. She was first diagnosed with SEF when she presented with abdominal pain where workup showed elevated Lipase 8,098 U/L (73-393 U/L) and Amylase 976 U/L (25-115 U/L). CT scans showed an ill-defined hypodense focus in the body of the pancreas, with incidental findings of a mixed intensity ovoid lesion in the left erector spinae, and heterogeneously enhancing ovoid masses in the left axilla, left lateral chest wall, left lower lung lobe, and the liver. Biopsy of the left axillary mass showed a round cell sarcoma consistent with Sclerosing Epithelioid Fibrosarcoma. PET scan confirmed widespread metastases to the lungs, pancreas, abdominal wall, left thigh and scalp. She underwent wide excision of the masses in the left axilla, thigh, and scalp. Adjuvant chemotherapy with Doxorubicin and Ifosfamide was then initiated. 6 months after starting treatment, she reported a rapidly enlarging anterior neck mass. She denied tremors, palpitations, any change in weight, heat/cold intolerance, changes in bowel movement, fatigue or muscle weakness. On physical examination there was a 2×2 cm, firm, non-tender, palpable nodule on the right thyroid lobe. Thyroid function tests were as follows: TSH 0.52 uIU/mL (0.55-4.78 uIU/mL), FT4 1.27 ng/dL (0.89-1.76 ng/dL), FT3 2.84 pg/mL (2.30–4.20 pg/mL). On thyroid ultrasound there was a 2.6×1.8×2.4 cm, mixed hypoechoic, solid, lobulated nodule in the upper to middle third of the right thyroid lobe, and a 0.3×0.2×0.3 cm hypoechoic solid nodule in the lower third of the left thyroid lobe. FNAB showed hypercellular smears with atypical round to spindle-shaped cells arranged in singly and loose to crowded clusters. She underwent total thyroidectomy, and histopathologic examination was consistent with a multifocal metastatic Sclerosing Epithelioid Fibrosarcoma. She was subsequently started on Levothyroxine replacement. CONCLUSION: This case, to our knowledge, is the first reported case of Sclerosing Epithelioid Fibrosarcoma (SEF) metastatic to the thyroid. Presentation: Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.