The biology and management of cartilaginous tumors: a role for targeting isocitrate dehydrogenase

Chondrosarcomas are rare mesenchymal neoplasms defined by the production of abnormal cartilaginous matrix. Conventional chondrosarcoma is the most common histology. The management of primary conventional chondrosarcoma generally is surgical with the possible addition of radiation therapy. Treatment of conventional chondrosarcoma is problematic in unresectable or metastatic disease because the tumors tend to be resistant to standard sarcoma chemotherapy regimens. Previous attempts at targeted therapy, including inhibitors of Hedgehog signaling, the mTOR pathway, and platelet-derived growth factor receptor (PDGFR) have been largely disappointing. However, heterozygous mutations in isocitrate dehydrogenase (IDH) enzymes recently have been identified in chondrogenic neoplasms, with mutations reported in approximately 87% of benign enchondromas, 70% of conventional chondrosarcomas, and 54% of dedifferentiated chondrosarcomas. The normal IDH protein continues to produce alpha-ketoglutarate (alpha-KG) whereas the mutant IDH protein converts KG to the oncometabolite 2-hydroxyglutarate (2-HG). Clinical trials of novel IDH inhibitors are ongoing, with evidence of early activity in IDH-mutant leukemias. IDH inhibitors show antitumor effects against IDH-mutant chondrosarcoma cell lines, supporting the inclusion of patients with chondrosarcoma with IDH mutations on IDH inhibitor clinical trials for solid tumors. Targeting IDH mutations may offer hope of a novel antineoplastic strategy not only for patients with chondrosarcomas, but also for other solid tumors with aberrant IDH activity.