*Brain Tumor Center at Erasmus MC Cancer Center, Erasmus MC, Rotterdam, The Netherlands; m.vandenbent@erasmusmc.nl oligodendroglioma: the early days Oligodendrogliomas have in particular attracted attention once it became clear that these are chemotherapy sensitive tumors. Although since the first description in 1926 and 1929 of oligodendroglial tumors it has been clear that these tumors are a special brand with a relatively good prognosis, they were taken for just another glioma subtype for many years thereafter [1]. Indeed, apart from a relatively more favorable prognosis of oligodendroglioma in comparison to their astrocytic counterparts and their often calcified lesions allowing a first diagnosis even at the time CT scans were not yet available, little pointed toward a specific significance for these tumors. This histological identification was somewhat complicated by the existence of another group with histological characteristics of both astrocytoma and oligodendroglioma, labeled mixed oligoastrocytoma. All these tumors were considered among the grade II and III glioma, and trials on grade II and high-grade glioma usually considered both astrocytoma, oligodendroglioma and mixed oligoastrocytoma. Furthermore, trials on high-grade glioma usually lumped both grade III and grade IV (glioblastoma) under the heading ‘anaplastic glioma’. As a consequence, grade III tumors were in general treated as grade IV tumors, albeit with the clear notion their outcome was better. oligodendroglioma: the chemotherapy sensitive glioma This clinical significance of the diagnosis ‘oligodendroglioma’ radically changed when Cairncross et al. in 1988 and again in 1992 reported remarkably high response rates to procarbazine, CCNU (lomustine) and vincristine (PCV) chemotherapy in relapsing anaplastic oligodendroglioma [2]. This lead to confirmatory Phase II studies, and subsequently to studies in newly diagnosed anaplastic oligodendroglial tumors [3,4]. At that time, still no distinction was made between pure oligodendroglial tumors and mixed oligodendroglioma. At least in part driven by the wish not to miss oligodendroglial tumors the percentage of patients with oligodendroglioma showed a steep incline, from 5% of all glioma in historical series to no less than 20% of all glioma cases [5]. A clear change in diagnostic criteria was part of that increase, already pointing to the lack of objective criteria for the histological diagnosis of glioma in general but more in particular of oligodendroglial tumors.