Epitheliod sarcoma: Molecular insights into proximal versus classic variant.

Abstract

e23552 Background: Epithelioid sarcoma (ES) is an ultra-rare sarcoma with distinctive pathologic and clinical features, marked by the loss of the expression of the SWI/SNF chromatin remodeling complex subunit SMARCB1. The current WHO classification recognizes two ES subtypes, different by morphology, clinical behavior and outcome: the “classic-type” and “proximal-type” ES. This study is aimed to better understand the molecular grounds sustaining this difference, and to identify new potential treatment targets to personalize therapy in this rare disease. Methods: RNA sequencing profiling was conducted on FFPE samples. Functional annotation enrichment was evaluated through over representation and gene set enrichment analyses (GSEA). Inference of immune contexture was obtained through deconvolution and single sample GSEA (ssGSEA) approaches. Results: Twelve samples from 5 proximal-type ES and 7 classic-type ES were profiled, 10 naïve and 2 pre-treated with chemotherapy. Proximal variant samples featured an overepresentation of MYC activity signatures and of other signatures impacting on cell cycle, protein synthesis and chromatin metabolism. Pathways enriched in the classic variant included NOTCH/HEDGEHOG and immune system regulation (e.g. inflammatory, interferon alpha and interferon gamma). Accordingly, deconvolution and ssGSEA approaches predicted an increased immune infiltration in classic subtype samples, essentially involving T cells, as well as increased expression of HLA class I molecules. Conclusions: Different regulatory networks seem to contribute to the different biologic and clinical behavior of proximal and classic ES. These preliminary data suggest a potential greater sensitivity of proximal type ES to drugs targeting the cell cycle, whilst immune checkpoint inhibitors might have some activity in classic variant ES. Further studies are ongoing to validate these preliminary observations.