The Observational EURACAN Prospective Clinical Registry Dedicated to Epithelioid Hemangioendothelioma: the Protocol of an International and Collaborative Effort on an Ultra-rare Entity

Given its incidence of 0.038/100 000/year, EHE is an ultra-rare sarcoma, with distinctive, well-defined pathological, molecular and clinical features. It belongs to the group of vascular sarcomas and is characterized by WWTR1-CAMTA1 (90%) or YAP1-TFE3 (10%) gene fusions, which represents today a hallmark for diagnosis. EHE potentially arises everywhere in the body and shows a high tendency toward metastatic spread, especially in the lung, liver and bone. The onset is characterized by different presentations, including a unifocal lesion (usually in the soft tissues), locoregional metastases (multiple lesions in a single organ or in a single anatomic compartment) and systemic metastases (multi-organ involvement). Also, the biological behavior of the disease is unique in sarcomas and variable, with spontaneous regressions reported, patients with untreated stable disease overtime, slowly progressive variants and highly aggressive and rapidly fatal cases. Today, the relative incidence of the different presentations is undefined, the natural history of the different subtypes is poorly understood, and reliable clinical or biological prognostic factors are lacking. Retrospective data suggest that patients with EHE presenting or developing during their course serosal involvement and / or effusion, systemic associated symptoms and anemia have a worse prognosis, but a prospective validation of this observation is lacking. In terms of management, surgery is the treatment of choice for localized disease, with an excellent outcome (expected cure rate of 70-80%) and no proven role for local or systemic adjuvant therapies. For patients with advanced, asymptomatic disease, active surveillance is often the upfront choice in order to minimize the risk of overtreatment. Systemic therapies are usually considered for patients with progressive or symptomatic disease, although a standard medical approach is currently not established. Unfortunately, conventional chemotherapy, including anthracycline-based regimens widely regarded as the mainstay in the treatment of advanced soft tissue sarcomas, showed marginal activity in EHE. The use of potentially active compounds, such as m-TOR inhibitors which proved the highest activity in EHE and could therefore represent the preferred option, is limited by regulatory constraints as they are not currently labeled in Europe for this indication. Given the degree of uncertainty on EHE management, a global consensus meeting was organized in December 2020 under the umbrella of the European Society for Medical Oncology (ESMO) involving > 80 multidisciplinary, worldwide experts together with a patient representative, with the aim of defining, by consensus, evidence-based best practices for the optimal approach to primary and metastatic EHE.

Since the number of patients is inherently low at the hospital level, the only way to increase knowledge about EHE and improve the diagnosis, treatment, and prognosis of this complex and heterogeneous disease is to harmonize and combine real-world data from sarcoma expert centres by leveraging a wide, international, joined effort. In this context, a unique opportunity is provided by the European Reference Networks (ERNs), virtual network established by the EU commission aiming to tackle rare conditions, including cancers. Among the three ERNs dedicated to cancer, EURACAN (https://euracan.eu) is the one focusing on the 10 families of rare adult solid cancers (RACs), including soft tissue sarcomas, bone sarcomas and gastrointestinal stromal tumour. Fostering academic research and promote epidemiological surveillance in rare cancers through setting up of shared registries is recognize as one of ERNs priorities. Within the sarcoma domain, taking into account the challenges described above, priority was given to ultra-rare sarcoma, and thanks to the strong connection, motivation and support provided by EHE Rare Cancer Charity UK, it was decided to start from EHE. We believe that in this context the collection of high-quality data by clinical registries will be crucial to improve the understanding of EHE natural history, validate and identify new prognostic factors, clarify the activity and efficacy of currently available treatment options and eventually provide and external control which might serve as a benchmark for the development of new drugs and support discussion with regulatory authorities.

The EURACAN EHE registry is a prospective clinical registry that will collect data from all new patients receiving a pathological and molecularly confirmed diagnosis of EHE starting from the 1st December 2023. To this aim, an EHE-focused clinical record form (CRF) was developed through the Research Electronic Data Capture (REDCap) and designed to capture the specific features of this disease.

For each patient, data collection will include:

1. A common baseline, including full details on demographic, comorbidities (special focus on immune-mediated and gynecological diseases), concomitant medications, physical examination, systemic symptoms at presentation, tumour-related pain assessment, blood tests, pathology and molecular features (on the diagnostic specimen), EHE extension at baseline (unifocal disease, loco-regional disease, systemic metastases)
2. Depending on the disease extent, detail on staging modalities, primary site and size, extension of metastatic disease (organs involved, number of lesions), presence and characterization of serosal involvement and effusion, treatment (surgery, radiation therapy, medical therapies, isolated limb perfusion, other locoregional techniques).