Epithelioid hemangioendothelioma: Real-world data about a rare entity in a Portuguese tertiary cancer center.

e23525 Background: Epithelioid hemangioendothelioma (EHE) is a rare entity of vascular origin, whose malignant potential is uncertain. It can develop in different locations, most commonly bone, liver and lungs. Since there are no specific associated symptoms, the diagnosis is often incidental. Due to its rarity there is no standard treatment. Our aim was to evaluate the demographic characteristics, course of disease and treatment effectivity in EHE patients in our institution in the last 25 years. Methods: We performed a retrospective study of all patients with EHE treated at our institution between January/1997 and September/2023. Statistical analysis was performed using SPSS. Normal distribution was checked using Shapiro-Wilk test. Results: From the 23 patients diagnosed with hemangioendothelioma, 20 were epithelioid (EHE) and 3 were other type. Of note, all the biopsies were centrally reviewed and since 2022 the diagnosis were confirmed with WWTR1 rearrange (3 out of 5 patients were positive). From the total number of EHE, the majority were women (n = 13, 65%). The mean age at diagnosis was 46 ± 22 years-old. Seven (35%) were asymptomatic and 13 (65%) had metastatic disease at diagnosis, all of them with lung metastasis, 2 (10%) with hepatic metastasis and 2 (10%) with bone metastasis. The most frequent primary locations were lungs (n = 5, 25%); soft tissue (n = 5, 25%), and liver (n = 4, 20%), followed by bone (n = 2,10%), stomach (n = 1, 5%), parotid gland (n = 1, 5%), superior vena cava (n = 1, 5%) and one case of unknown primary EHE. The majority of tumors were multifocal (12, 60%). Eight (40%) patients were under active surveillance, 4 (20%) underwent surgery with or without adjuvant radiotherapy, 2 (10%) underwent systemic treatment with tyrosine kinase inhibitor (pazopanib) and 2 (10%) chemotherapy (paclitaxel, doxorubicin). Two (10%) patients received a liver transplant and 2 (10%) patients underwent multiple treatment modalities. With a median follow-up of 30.89 months (3-253), 6 (30%) patients were dead at the time of analysis and mean overall survival was 142.3 months. Patients with an angiosarcoma differentiation had significantly worse mean survival outcomes (p < 0.001), 7.9 ± 4.5 months vs. 158.9 ± 37.2 months. Conclusions: The biological behavior of these tumors remains uncertain. In our cohort, the majority of patients presented with distant metastasis, but the course of the disease was very heterogeneous, regardless of the primary or metastatic site or the treatment modality. Our data emphasizes that this disease should be managed on a case-by-case basis, with a multidisciplinary approach and tailored treatment and surveillance.