[Oligodendrogliomas: their morphological characteristics and molecular alterations]

Oligodendrogliomas constitute a group of infiltrating gliomas with a good response to radio and chemotherapy, which makes it important to distinguish them from the other gliomas and more especially from astrocytomas. Although oligodendrogliomas generally present typical histological features and are easy to diagnose, they sometimes have a mixed or hybrid morphology that makes their classification difficult and ambiguous. In these cases immunohistochemistry is of little use, since to date no markers have been found that enable a reliable distinction to be made between oligodendrogliomas and astrocytomas.

Here we review the histological criteria of oligodendroglial tumours and how to distinguish them from other morphologically similar brain tumours. We also discuss how alterations to the short arm of chromosome 1 and to the long arm of chromosome 19 (co-deletion of 1p/19q), which can be detected using FISH or PCR, enable us to classify mixed oligoastrocytic tumours and to define subgroups of oligodendrogliomas with different prognoses and responses to treatment.

In daily practice, the status of 1p and 19q should be analysed in all tumours with an oligodendroglial histological phenotype, because this makes it possible to define subgroups each having different prognoses and responses to therapy.