Prolonged benefit to pembrolizumab in anaplastic oligodendroglioma patient with mismatch repair deficiency: a case report.

High-grade gliomas, including anaplastic oligodendroglioma, represent the most common malignant neoplasms of the central nervous system in the adult. The standard treatment of anaplastic oligodendroglioma consists of maximum surgical resection, radiotherapy and subsequent chemotherapy. Despite multimodal treatment, theoretically, all cases can relapse. Immune checkpoint inhibitors (ICIs) as pembrolizumab demonstrated promising results in many types of tumors, particularly in the presence of mismatch repair deficiency (MMRd). However, no ICI benefit was demonstrated in high-grade glioma prospective studies, although no biomarker was analyzed. Here, we describe an interesting case of recurrent anaplastic oligodendroglioma with MMRd, reporting a prolonged disease stability during pembrolizumab treatment.