Exploring Emerging Therapeutic Targets in Osteosarcoma by Revisiting the Immune and Cancer-Intrinsic Hallmarks of Cancer

Osteosarcoma (OSA) is an aggressive primary bone cancer mainly affecting the pediatric population. Despite intensive multimodal treatments, therapeutic progress has remained limited for decades, resulting in high recurrence rates, poor prognosis driven by metastatic progression, and severe chemotherapy-associated toxicities. To advance the development of more effective and safer therapeutic strategies, our recent studies identified Chondroitin Sulfate Proteoglycan (CSPG)4 as a relevant mediator of the malignant behavior of OSA cells. Targeting CSPG4 DNA-based vaccine demonstrated encouraging antitumor activity against OSA. Nevertheless, since single-agent immunotherapies are often constrained by tumor immune escape, the need for rational combinatorial strategies is of utmost importance. In this perspective, we broaden our analysis to include other potentially complementary targets beyond CSPG4, which may contribute to OSA pathogenesis. Among these, the cystine/glutamate antiporter xCT and Toll-like Receptor 2 (TLR2) emerge as particularly promising due to their established role in tumor progression, therapy resistance, and immune modulation. We discuss the contribution of all these molecules in major hallmarks of OSA-(1) proliferative and survival advantages, (2) metastasis and angiogenesis, and (3) immune evasion-and examine potential strategies for their combined targeting. By leveraging knowledge gained from other cancer models and integrating it with the distinct biological and clinical features of OSA, this perspective seeks to outline rational and innovative combinatorial strategies that may overcome current therapeutic limitations and ultimately improve patient outcomes.