Epitheliod hemagioendothelioma (EHE) patient-derived model (PDX): Drug activity assessment and validation of novel biomarkers.

11566 Background: EHE is an ultra-rare sarcoma marked by two specific fusions, WWTR1-CAMTA1 (̃90%) and YAP1-TFE3 (̃10%). The clinical course of EHE ranges from indolent to highly aggressive, often associated with systemic paraneoplastic symptoms. Molecular predictors of clinical outcome are unknown. While surgery is the mainstay of treatment in the localized setting, management of advanced disease is challenging due to the rarity and poor sensitivity to conventional chemotherapy. This hampers the conduct of large prospective clinical trials. We report herein the first available EHE PDX (developed at the Istituto Nazionale Tumori, Milan, Italy) (INT), to assess the activity of old and new anticancer agents in EHE and inform future clinical studies. We also report on the preliminary results of a prospective observational study, ongoing in collaboration with The EHE Rare Cancer Charity (UK) and The EHE Foundation (US) aimed at identifying prognostic factors. Methods: A PDX of EHE in SCID mice was generated at INT from a patient (pt) suffering with the aggressive clinical variant, presenting with systemic symptoms. The PDX fully reproduces the originating clinical tumor in terms of morphology, biology ( WWTR1- CAMTA1 positive), overall transcriptomic profile. 2D (monolayer) and 3D (sferoids) cell cultures were established following PDX disaggregation. We have started assessing the comparative activity of currently available drugs (doxorubicin, sirolimus), while the efficacy of novel agents is undergoing. In parallel, we analyzed the presence of a selection of inflammatory cytokines in prospectively collected blood samples from EHE pts who entered an international observational study and we looked at their presence and modulation in the PDX model. Results: PDX experiments showed almost negligible activity of doxorubicin while sirolimus induced an 80% tumor volume inhibition. Biochemical analysis in tumors explanted from sirolimus-treated mice confirmed the down-regulation of mTOR downstream signaling. Among all cytokines, Growth and Differentiation Factor-15 (GDF-15) was found significantly over-expressed in serum of EHE pts (n = 23), particularly those with the most aggressive clinical variant, compared to healthy subjects (n = 23; p< 0.01). Consistently, EHE PDX and cell culture were found to release in the blood/culture medium GDF-15. Sirolimus was found to down-regulate GDF-15 release in both in vivo and in vitro EHE models. Conclusions: Our preliminary results indicate that this EHE PDX model is suitable i) for comparatively assessing the activity of anticancer drugs, and ii) for identifying and pre-clinically validating novel biomarkers. The role of GDF-15 in EHE progression deserves further investigation.