Given that isocitrate dehydrogenase (IDH) 1/2-mutated gliomas (II/IV) have been associated with poor outcomes, and that IDH 1/2-glioma cells promote the synthesis of so-called oncometabolites such as D2-hydroxyglutamate (D-2HG), which are potentially responsive to metformin, an ongoing dose-finding phase 1b/2 trial determined the efficacy and toxicity of a combined drug protocol consisting of metformin and chloroquine (CQ) in IDH1/2-mutated HGG, high-grade chondrosarcoma and intrahepatic cholangiocarcinoma. The gene discussed is IDH1; the disease is central nervous system cancer.