(P 153) PATTERNS, MANAGEMENT AND SURVIVAL OUTCOMES OF PATIENTS WITH EPITHELIOID HEMANGIOENDOTHELIOMA: A NATIONWIDE ANALYSIS FROM THE CANADIAN SARCOMA RESEARCH AND CLINICAL COLLABORATION DATABASE

Objective: Epithelioid Hemangioendothelioma (EHE) is an ultra-rare sarcoma, affecting approximately one in a million individuals. It is characterized by WWTR1-CAMTA1 gene fusion in >90% of cases. Its clinical behaviour can vary from indolent to aggressive. Because of the scarcity of cases, we aim to describe the presentation, management, and clinical outcomes of Canadian EHE patients (pts).

Methods: Data was obtained retrospectively from the Canadian Sarcoma Research and Clinical Collaboration (CanSaRCC) database. EHE patients, diagnosed from November 1993 to July 2023 across 9 Canadian sites were included in this series. Clinical presentation, treatment and clinical outcome, including survival data were collected. Kaplan-Meier was used to estimate overall survival (OS) and event-free survival (EFS). Cox regression was used to estimate factors influencing survival outcomes.

Results: One hundred and ninety eight (n=198) pts were identified and included in this series (Table 1). Molecular testing (e.g. WWTR1-CAMTA1, YAP1-TFE3) were performed in 54 pts, of which in 43 pts, were positive. Since 2015, only 48 cases, out of 99 (48.5%) were subjected to molecular testing. In 61 pts (31%), the diagnosis of EHE was incidental. The most frequent primary sites were the liver (n=56 [28.3%], extremities (n=31 [15.7%]) and lungs (n=27 [13.6%]). Ninety-four (n=94 [47.5%]) of pts were diagnosed with metastatic disease initially. Pleural effusion was present in 63 (31.8 %) pts while ascites was seen in 25 (12.6%) pts. Treatment intervention were recorded for 136 pts. In the advanced, incurable setting, fifty five (27.8%) pts received at least one systemic therapy (median lines of therapy 1, range 1-6). Sirolimus and pazopanib were most common drugs used in first and second line, respectively (Table 2). With a median follow-up of 4.4 years (range 0.14-28.5 years), the median OS was 8.6 years (95% CI 5.4 – 16.5) while median EFS was 5.5 years (n=198, 95% CI 3.4 – 8.5). In multivariate analysis, older age, pleural effusion, ascites, primary lung disease, and metastatic disease were associated with unfavorable survival (Table 3).

Conclusion: This dataset provides insight into the management and survival outcomes of EHE pts in Canada. Molecular testing rate, since its initial use in 2015, is still low at less than half patient diagnosed. Most patients present with a liver primary. Unfavorable survival outcomes were associated with pleural effusion, ascites, and primary lung disease. The rate of use of systemic therapy is low, possibly reflected by disease biology and lack of effective agents.