The Osteosarcoma Tumor Microenvironment: From Cellular Interactions to Advanced Preclinical Models.

OS is the most common primary malignant bone tumor, predominantly affecting children, adolescents, and young adults. Despite advances in multimodal treatment, patient outcomes have remained largely unchanged over the past decades, particularly in cases of metastatic or recurrent disease. Increasing evidence highlights the pivotal role of the tumor microenvironment (TME) in OS progression, metastasis, immune evasion, and therapeutic resistance. The OS TME comprises a complex and dynamic network of tumor cells, immune cells, cancer-associated fibroblasts, mesenchymal stromal cells, endothelial cells, extracellular matrix components, and soluble factors that collectively regulate tumor behavior. This review summarizes the current understanding of the OS TME, highlighting the interactions between malignant cells and their surrounding microenvironment and their contribution to tumor growth, angiogenesis, invasion, metastatic dissemination, and treatment response. Moreover, here we discuss the strengths and limitations of the most relevant preclinical models currently used to investigate OS biology and evaluate novel therapeutic strategies. Three-dimensional (3D) culture systems, including spheroids, organoids, and biomimetic scaffold-based models, today are considered the models able to best recapitulate the structural, mechanical, and cellular complexity of the native tumor microenvironment than conventional two-dimensional cultures. In addition, patient-derived xenograft (PDX) models are reviewed for their ability to preserve the histopathological, molecular, and genetic characteristics of the original tumors, making them valuable platforms for translational research, biomarker discovery, and personalized medicine.