Oligodendroglioma: Toward molecular definitions in diagnostic neuro-oncology

Oligodendroglial tumors have attracted great interest in both basic and clinical neuro-oncology over the past decade. This interest is mainly due to the clinical observation that anaplastic oligodendrogliomas and anaplastic oligoastro-cytomas, in contrast to the vast majority of anaplastic astrocytomas and glioblastomas, frequently respond favorably to chemotherapy. In addition, oligodendroglial tumors are associated with longer survival times than the diffuse astrocytic gliomas. These differences in response to therapy and in prognosis have been associated with distinct genetic aberrations, in particular the frequent loss of alleles on chromosome arms 1p and 19q in oligodendroglial tumors. In addition, other genetic changes have been reported as indicators of poor response to therapy and short survival, including homozygous deletion of the CDKN2A gene at 9p21, mutation of the PTEN gene at 10q23, and amplification of the EGFR gene at 7p12. In this review we summarize the current state of the art concerning the molecular genetics of oligodendroglial tumors. A particular focus is placed on the role of molecular genetic findings in the diagnostic and prognostic assessment of these neoplasms. As a result of the recent advances in the field, we propose that clinical decisions in the management of patients with oligodendroglial tumors should be based on the combined assessment of clinical and neuroimaging features, histological classification and grading, as well as molecular genetic characteristics.