EXT2 promotes sarcoma progression and immune evasion via the AKT/c-Myc/PD-L1 axis: a multi-omics and validation study

Sarcomas are a heterogeneous group of mesenchymal malignancies with diverse histological subtypes, limited treatment options, and generally poor outcomes in advanced disease. EXT2, a glycosyltransferase involved in heparan sulfate biosynthesis, has been implicated in tumor–microenvironment interactions, but its role in sarcoma progression and immune regulation remains incompletely understood. We integrated transcriptomic, epigenomic, and immune landscape analyses across public sarcoma datasets and clinical specimens to investigate the clinical and biological relevance of EXT2. Functional effects of EXT2 were assessed using in vitro assays, in vivo tumor models, and CD8+ T-cell co-culture systems. Single-cell RNA sequencing data were analyzed to localize EXT2 expression within the tumor microenvironment. EXT2 was consistently upregulated in sarcoma tissues and associated with unfavorable survival outcomes, with particularly consistent evidence in osteosarcoma cohorts. EXT2 silencing suppressed tumor cell proliferation, migration, invasion, and in vivo growth, accompanied by reduced AKT phosphorylation, c-Myc expression, and PD-L1 levels. EXT2-high tumors exhibited features of an immune-excluded microenvironment, including reduced CD8+ T-cell infiltration and enrichment of cancer-associated fibroblasts and M2-like macrophages. Although EXT2 expression was associated with higher tumor mutational burden and microsatellite instability, EXT2-high tumors showed predicted immune exclusion and reduced responsiveness to immune checkpoint blockade. Single-cell analyses localized EXT2 predominantly to stromal and endothelial compartments. These findings identify EXT2 as a clinically relevant regulator of sarcoma progression and immune modulation. By engaging an AKT/c-Myc/PD-L1 signaling axis and shaping an immune-excluded tumor microenvironment, EXT2 may serve as a prognostic biomarker and a potential therapeutic target in selected sarcoma subtypes, warranting further subtype-specific and mechanistic investigation.