INTRODUCTION: Chondrosarcoma (CHS) is a malignant cartilaginous tumor representing the most common primary bone cancer in adults.[1] Due to its dense chondrogenic extracellular matrix and hypoxic environment, CHS is highly resistant to conventional chemotherapy and radiation.[2] Development of multimodal imaging to characterize and map in vivo CHS microenvironment is fundamental for specific diagnosis and personalized therapy. In this work, we proposed to combine the resolution of chemical exchange saturation transfer (CEST) MRI with nuclear imaging sensitivity to improve CHS microenvironment understanding.[3] METHODS: Swarm rat CHSs were implanted subcutaneously in NMRI nude mice (n=10). When tumors were measurable (12-16 days post-transplant), mice were imaged by CEST MRI.[4] Proteoglycans, the main component of chondrogenic extracellular matrix, were quantified by GAG CEST contrast. Guanidyl-and APT CEST contrasts were combined to characterize acidic pH, as hypoxia reflect. These two features, proteoglycans and hypoxia, were assessed in parallel by nuclear imaging with 99m Tc-NTP 15-5 SPECT imaging [5] and