(P 384) REAL WORLD EXPERIENCE IN TREATING HEPATIC EPITHELIOID HEMANGIOENDOTHELIOMA: AN ULTRA-RARE VASCULAR TUMOR

Objective: Hepatic epithelioid hemangioendothelioma (HEHE) is an ultra-rare vascular tumor with an incidence of one per million worldwide, thus little consensus exists for optimal multimodality treatment paradigms including surgical, locoregional, and systemic therapies. The purpose of this observational study involving one of the largest single-center experiences with HEHE is to highlight the stage-dependent outcomes following various treatment modalities for this rare cancer.

Methods: This single-institution study included all patients with a histopathologic diagnosis of HEHE from 2000-2024. Patient demographics, staging, treatment, and survival data were gathered from electronic medical records. Overall survival (OS) data analysis and Kaplan-Meier curves were generated using Stata SE 18.0 (StataCorp LLC, College Station, TX).

Results: The study cohort included 19 patients with HEHE; 57.9% female; 89.5% Caucasian, 5.3% African American, and 5.3% unknown race or ethnicity. The median age at time of diagnosis was 58 years (range, 24-86). Three patients had a solitary hepatic-only tumor, and 16 patients had multifocal liver disease. According to AJCC staging, 7 pts were stage IB, and 6 were stage IV with synchronous pulmonary metastases as the most common pattern of distant disease. Local therapy included liver resection (N=8), stereotactic external beam radiation therapy (N=1), and selective arterial-based liver directed radiation (y90) therapy (N=1). No patient received a liver transplant. Eleven patients received systemic therapy with mTOR inhibition with sirolimus as the most common (N=5) with a median duration of treatment of 14 months. Three patients remain on sirolimus with either stable disease or partial response. Other systemic agents included doxorubicin, paclitaxel, cisplatin, cyclophosphamide, vincristine, nivolumab, bevacizumab, pazopanib, and two phase I experimental agents. Two patients declined any treatment. The mean number of lines of systemic therapy for patients with metastatic disease was 3.8 and 0.5 in nonmetastatic cases. The median follow-up for all patients was 22.1 months (range, 0.5-72) after time of diagnosis. Patients with stage IV HEHE had a median overall survival (OS) of 26 months (range, 12.9-41.7), while patients without systemic metastases had a 5-year OS of 66.7%. Kaplan-Meier curves for patients with and without systemic metastases are shown in Figure 1.

Conclusion: The natural history and treatment outcomes for HEHE are not well established in the literature. This single-institution observational study suggests improved outcomes after liver resection for HEHE without extrahepatic metastases. There remains significant opportunity for improving outcomes in patients with metastatic disease, particularly in optimization of systemic therapies. Larger multi-institutional cohort studies and meta-analyses are needed to guide future treatment paradigms.