Introduction: Mutations in isocitrate dehydrogenase 1 and 2 (IDH1/2) are common in gliomas and result in enzymes that produce D-2-hydroxyglutarate (D-2-HG). The purpose of this study is to evaluate the ability of microthrombi (MT) to predict isocitrate dehydrogenase 1 or 2 (IDH1/2) mutation status, and to act as a new histologic criterion for the diagnosis of glioblastoma. Routine neuropathologic evaluation led to the discovery that IDH1/2-mutant gliomas do not usually contain micro thrombi.
Methods: We screened 317 World Health Organization (WHO) grade II-IV gliomas for microthrombi in discovery and validation cohorts at 2 separate institutions. Gliomas were analyzed from The Cancer Genome Atlas for TF gene promoter methylation and mRNA levels. A tissue microarray (TMA) of patient-derived gliomas was analyzed for TF expression via immunohistochemistry. We evaluated human platelets and blood for aggregation and clotting time, respectively, in the presence of D-2-HG.
Results: Whereas 86% of WT-IDH1/2 gliomas had Microthrombi, only 2-4% of mut-IDH1/2 gliomas did and were the most powerful predictor of IDH1/2 mutation. In terms of prognostic strength microthrombus was comparable to necrosis and microvascular proliferation, which currently are the only WHO criteria for a pathologic diagnosis of grade IV glioblastoma. Mutant IDH1/2 gliomas had TF gene promoter hypermethylation and dramatically reduced TF expression. D-2-HG inhibited platelet aggregation by blocking intracellular calcium accumulation and in human blood, D-2-HG lowered free calcium by up to 40% and doubled clotting time. Finally, 25%-30% of patients with a wild-type glioma developed systemic hyper coagulation at both institutions, in contrast to no patients with a mutant glioma.
Conclusions: Mutant IDH1/2 enzymes have potent antithrombotic activities within gliomas and throughout the systemic circulation. This has profound implications for the pathologic evaluation of gliomas, the effect of altered metabolism on tumor microenvironment, and the postoperative management of these patients.
Patient Care: Thromboembolic events occur in 10-30% of high-grade glioma patients, and have been linked to TF-containing microparticles released by the tumor into the circulation. Mutant IDH1/2 gliomas not only have less TF and intratumoral microthrombi, but also have a dramatically reduced risk of systemic hypercoagulation. Mutation screening can thus help identify patients in need of careful monitoring and prophylaxis.
Moreover, this study has a tremendous impact on the pathologic workup of gliomas as well as postoperative care, and advances our understanding of how IDH1/2 mutations affect glioma biology.
Learning Objectives: By the conclusion of this session, participants should be able to: 1) describe a powerful new mechanism of action by mutant IDH1/2 on the microenvironment. 2) Identify micro thrombus, which is the most powerful clinical or histologic predictor of IDH1/2 mutations reported to date, and is also a strong prognostic marker. 3) Understand the interactions between the genome, the epigenome, metabolism, and the microenvironment.