Pharmacologic Resistance in Soft Tissue Sarcomas: Mechanisms, Biomarkers, and Translational Therapeutic Strategies

Soft tissue sarcomas are rare, biologically diverse mesenchymal malignancies in which pharmacologic resistance cannot be explained by a single unifying mechanism. In this narrative review, resistance is conceptualized as a dynamic, multilayered process shaped by histologic subtype, genomic architecture, transcriptional plasticity, the tumor microenvironment, and treatment-driven selective pressure. Resistance to conventional chemotherapy arises through both intrinsic and acquired mechanisms, including altered drug transport and metabolism, enhanced DNA damage responses, impaired apoptotic signaling, clonal selection, and the emergence of therapy-persistent cellular states. By contrast, resistance to targeted and epigenetic therapies more often reflects adaptive bypass signaling, lineage reprogramming, and incomplete identification of subtype-specific dependencies than secondary on-target alterations alone. The tumor microenvironment further contributes to therapeutic failure through hypoxia, extracellular matrix-mediated barriers, abnormal vascularization, myeloid-dominant immunosuppression, and immune exclusion, thereby helping explain the modest and histology-dependent activity of immune checkpoint inhibitors in soft tissue sarcoma. This review also differentiates baseline predictive biomarkers from dynamic resistance-monitoring tools, underscoring the potential—despite still limited clinical maturity—of pharmacogenomic markers, immune signatures, tertiary lymphoid structures, circulating tumor DNA, and circulating methylation-based approaches. Finally, emerging strategies to overcome resistance are examined, including mechanism-based combinations, biomarker-guided treatment selection, synthetic lethality, functional precision platforms, and adaptive histology-specific trial designs. Collectively, these observations support a view of resistance in soft tissue sarcoma as a context-dependent biological process that demands integrated, subtype-aware, and translationally grounded therapeutic strategies.