Oligodendrogliomas: Molecular Biology and Treatment

ABSTRACT
Oligodendroglial tumors continue to receive much attention
because of their relative sensitivity to chemotherapy.
The histological diagnosis of oligodendroglial
tumors is subject to considerable interobserver variation.
The revised 2007 World Health Organization
classification of brain tumors no longer accepts the
diagnosis “mixed anaplastic oligoastrocytoma” if necrosis
is present; these tumors should be considered
glioblastomas (perhaps with oligodendroglial features).
The 1p/19q codeletion that is associated with
sensitivity to chemotherapy is mediated by an unbalanced
translocation of 19p to 1q. Randomized studies
have shown that patients with 1p/19q codeleted tumors
also have a better outcome with radiotherapy.
Histologically more atypical tumors are less likely to
have this 1p/19q codeletion; here, other alterations
usually associated with astrocytic tumors are often
found. Some patients with tumors with classic histological
features but no 1p/19q codeletion still have a
very favorable prognosis.
Currently, the best approach for newly diagnosed
anaplastic oligodendroglial tumors is unclear. Early ad
juvant chemotherapy does not provide a better outcome
than chemotherapy at the time of progression. The
value of combined chemoirradiation with temozolomide
has not been proven in these tumors, and could at least
theoretically be associated with greater neurotoxicity.
Tumors with 1p and 19q loss can also be managed with
early chemotherapy, while deferring radiotherapy तो
the time of further progression. The presently available
second-line chemotherapy results are modest, and better
salvage treatments are necessary. The molecular explanation
for the greater sensitivity of 1p/19q codeleted
tumors is still unclear, and this could, in part, be explained
by more frequent MGMT promoter gene methylation.
The Oncologist 2009;14:155–163