Synovial sarcoma in children and adults: tumor microenvironment and microRNAs as predictors of metastasis

Synovial sarcoma is among the most aggressive soft-tissue sarcomas and carries a high risk of early metastasis. This review summarizes data from 2015–2025 on the role of the tumor microenvironment and microRNAs in shaping the metastatic potential in both children and adults with this pathology. Predominance of M2 macrophages, low CD8+ T-cell infiltration, and activation of the programmed cell death 1 (PD-1)/programmed death-ligand 1 (PD-L1) and CD47–SIRPα axes create an immunosuppressive niche that promotes tumor dissemination. Deregulated microRNAs – including tissue, circulating, and exosomal species – enhance angiogenesis, drive epithelial-mesenchymal transition, and modulate immune responses. These factors underpin emerging prognostic models and therapeutic strategies, including immunotherapy and anti-miRNA interventions.