Cerebral oligodendrogliomas in adults and children. Current data and perspectives

Cerebral oligodendrogliomas represent more than 30% of glial tumors in adults. Mean age at diagnosis is 41 for grade A and 45(1/2) for grade B, epilepsy being the main revealing symptom (91.5% of A, 76% of B). Survival at 5, 10 and 15 years is respectively 75.5%, 51% and 22.4% for grade A (median: 136 months), and 45.2%, 31.3% and 0% for grade B (median: 52 months). It is influenced by age at diagnosis: median, before 40 years of age, is 12 years for A and 8(1/2) for B; between 40 and 60, is 12 years for A and 4(1/2) for B; over 60, is 4 years for A and 1(1/2) for B. In children, they represent less than 2.5% of cerebral tumors and include 23% grade A and 77% grade B (48.5% WHO grade II and 51.5% WHO grade III). Mean age at surgical removal is 9.5 +/- 5 years. One third are hemispheric, 2/3 are revealed by epilepsy. A complete surgical removal is performed in 60%. Mean survival is 13 years (154 +/- 20 months), with a mortality at 5 and 10 years of 60% +/- 9%, and a risk of recurrence of 54% +/- 9% at 5 years and 46.5% +/- 10.5% at 5 years. The main differential diagnosis of grade A oligo is dysembryoplastic neuroepithelial tumors (DNT). Inversely, thalamic locations, most often grade B, generally present with a motor deficit; complete removal can be achieved in only 15%. The only efficient treatment is chemotherapy, requiring search for chemosensitivity (1p19q deletion, expression of MGMT gene, analysis by MR-spectroscopy and TEP). Logically, surgical debulking should be as wide as possible, but with preservation of neurological and cognitive functions with the help of modern imaging progresses (fMRI, diffusion and perfusion MRI, tractography, PET) and operative techniques (navigation, cortical stimulation, and even opertaive MRI). Tumors presenting clinical and radiological progression should be removed. Operative mortality varies from 0 to 6%, transient morbidity from 20 to 25%, definit morbidity from 5 to 10%. Radiotherapy does not significantly modify survival whatever the delivered dose. The important point is the patient's radiosensitivity: survival is 148 months for radiosensitive patients versus 12 months for non responsive patients. Studies and development of pretherapeutic assays of tumoral radiosensitivity will be a fundamental research axis (PET, sample studies).