C79-22 Epithelioid Hemangioendothelioma of the Anterior Mediastinum With Multiorgan Metastatic Progression in a Young Adult: A Case Report

Introduction Epithelioid hemangioendothelioma (EHE) is a rare malignant vascular tumor with highly variable clinical behavior, and primary mediastinal presentation is extremely uncommon, often presenting as an incidental finding. Due to its rarity, diagnosis and management remain challenging, which contributes to the absence of an established systemic therapy with proven efficacy. Case presentation A 35 year old male, previously healthy, was referred after an abnormal routine chest radiograph. Computed tomography revealed a large anterior mediastinal mass measuring 107 × 92 × 105 mm, encasing vascular structures and adjacent to the thymus and pericardium. Video-assisted thoracoscopic resection with thymectomy and partial pericardiectomy was performed. Histopathological examination demonstrated epithelioid hemangioendothelioma, FNCLCC grade 2, with 20% necrosis and focal positive margins (pT3N0). Postoperatively, the patient received adjuvant external beam radiotherapy (52.2 Gy total). Despite initial radiologic stability, follow-up imaging revealed metastatic progression, including pulmonary lymphangitic involvement, hepatic lesions, and multifocal osseous disease affecting the sacroiliac joints and vertebral bodies. Systemic therapy with pazopanib (400 mg twice daily) was initiated; however, treatment adherence was limited and radiologic progression continued. Given the lack of effective systemic therapeutic options, the disease course advanced to symptomatic respiratory decline. The patient is currently receiving multidisciplinary palliative care and localized radiotherapy for symptom control. Discussion Primary mediastinal EHE is exceptionally rare and often presents incidentally in asymptomatic patients. Complete surgical resection remains the mainstay of localized disease; however, positive margins and large tumor burden are associated with higher recurrence risk. Systemic therapy options, including multikinase inhibitors and mTOR inhibitors, demonstrate modest and inconsistent responses. Disease progression in this case highlights the aggressive potential of EHE despite early intervention. Conclusion Mediastinal EHE should be considered in the differential diagnosis of anterior mediastinal masses, particularly in young adults without respiratory symptoms. Early multidisciplinary evaluation and long-term surveillance are essential, though effective systemic treatment remains an unmet need. Funding None. Conflicts of Interest: The presenting author declares no relevant conflicts of interest.