Combined Diffuse Astrocytoma and Pleomorphic Xanthoastrocytoma Grade III Sharing IDH1 R132H Mutation

BACKGROUND: Collision tumors are often difficult to distinguish from intratumoral heterogeneity in diffuse gliomas. CASE DESCRIPTION: We report the case of a 44-year-old woman admitted for intracranial hypertension. Magnetic resonance imaging revealed a right intra-axial frontal mass, composed of a hypervascular nodular portion contrasting with a large nonenhanced infiltrative and muliticystic portion. Histopathologic examination showed the occurrence of two morphologically different gliomas. The largest component corresponded to an anaplastic astrocytoma, IDH1-mutated. The second corresponded to a leptomeningeal nodule, reminiscent of a pleomorphic xanthoastrocytoma. Both tumoral components exhibited anaplastic features, World Health Organization grade III. Immunohistochemical and molecular studies showed that the 2 components were identical, IDH1 R132H mutated but without BRAF V600E mutation. Tumor progression was assessed 2 years after surgery, after radiotherapy and chemotherapy, showing supratentorial leptomeningeal dissemination. CONCLUSIONS: Collision tumors and combined neoplasms have been rarely described in the brain and only 4 similar articles report the synchronous occurrence of 2 primary gliomas. A review of the literature is proposed, focusing on criteria that could be used to discriminate them.