Oligodendroglioma: pathology and molecular biology

Recently, important new information has become available concerning the histologic recognition and molecular biology of oligodendrogliomas. This information, in turn, impacts the way neurosurgeons diagnose and treat patients with these tumors. The purpose of this paper is to review the pathology and basic science of oligodendroglioma, highlighting these developments.

Information for this review was obtained by a Medline search using the term "oligodendroglioma," and limiting the results to articles dealing with pathology. Chapters from standard textbooks were also used, and bibliographies were checked for additional key articles contributing to the understanding of the pathobiology of this disease.

On histologic examination, oligodendrogliomas must be differentiated from tumors including the fibrillary astrocytoma, clear cell ependymoma, central neurocytoma, and dysembryoplastic neuroepithelial tumor (DNT). There is no specific immunocytochemical marker allowing for the recognition of human oligodendroglial tumor cells. A current simplified grading scheme separates these tumors into low grade (WHO grade II) and anaplastic (WHO grade III) oligodendrogliomas. New molecular and genetic markers may aid in grading oligodendrogliomas and identifying patients with a better prognosis or response to chemotherapy. Markers studied include Ki-67, PCNA, EGFr, VEGF, platelet-derived growth factor, p16, p18, p53, bcl-2, COX-1, and chromosomal deletions. The combination of allelic losses on chromosomes 1p and 19q has been statistically associated with a longer recurrence-free survival after chemotherapy.

A patient with an oligodendroglioma may at times still present a diagnostic challenge for the neuropathologist. Yet making an accurate diagnosis is essential, since the clinical course and optimal therapeutic approach differs from that of other gliomas. In the near future, molecular characterization of oligodendrogliomas is expected to play an even greater clinical role.