Heterogeneity in epithelioid hemangioendothelioma (EHE): Insights into common and organ-specific tumor pathways.

Abstract

11565 Background: EHEs are ultra-rare sarcomas that can arise from various organs, with the primary site being an important prognostic factor. We hypothesized that EHEs from different organs harbor heterogeneous tumor cells. Understanding key pathways associated with this heterogeneity may lead to improved therapies for EHE patients. Methods: EHE samples from different primary sites with confirmed pathognomonic gene rearrangements were analyzed. Spatial transcriptomics was performed on FFPE samples using the Visium CytAssist platform. Pathway analyses were conducted with AUCell, and cell compositions were estimated using XCell. A second platform, Xenium, was used for confirmation. Results: Eight EHE patients with different primary organ sites (liver 3, lung & pleura 2, bone 2, soft tissue 1) and gene rearrangements (CAMAT1 FISH+ 6, TFE3 FISH+ 1, WWTR1 FISH+ 1) had spatial transcriptomic results. Unsupervised clustering identified 35 different clusters and EHE clusters were defined in accordance to histology and vascular markers (CD31, CD34, and ERG). These clusters could be broadly categorized into “common (non-organ-specific)” clusters, observed in three or more organ types, and “organ-specific” clusters. Common clusters showed higher levels of stem-like endothelial cell markers and increased TGF-beta and mTORC1 pathway activity, which may explain the clinical benefit of sirolimus in EHE. Using liver EHEs as an example, the liver-specific cluster demonstrated a fibroblast/mesenchymal stromal cell differentiation pattern not observed in EHEs from other organs. GDF-15, which is associated with aggressiveness in EHE and cachexia, was significantly higher expressed in common than organ-specific cluster. In liver and bone EHEs, clusters with high GDF-15 expression tend to have higher TGF-beta signaling and lower dendritic cells, implying the role of GDF-15 in EHE with immune regulation. These findings were validated in Xenium analysis. Conclusions: This study shows that EHE tumors share certain core pathways but also exhibit organ-specific differentiation patterns, which may underlie their variable prognoses. The coexistence of both “common” and “organ-specific” clusters highlights the importance of personalized treatment strategies and paves the way for more targeted therapeutic development in EHE.