La présence de délétion 1p et 19q est réputée corrélée au diagnostic d’oligodendrogliome, à une plus grande chimiosensibilité et à un meilleur pronostic. Nous avons revu la littérature afin d’évaluer l’utilité de ces corrélations en pratique clinique. Après analyse de 33 études incluant 2666 patients, les taux moyens de délétion 1p et de codélétion 1p19q étaient respectivement 65,4 et 63,3 % dans les oligodendrogliomes, 28,7 et 21,6 % dans les oligoastrocytomes, 13,2 et 7,5 % dans les astrocytomes, 11,6 et 2,9 % dans les glioblastomes. La présence de délétions 1p ou de codélétions constitue un argument fort en faveur d’un diagnostic histologique oligodendroglial, mais leur absence ne permet pas d’éliminer le diagnostic d’oligodendrogliome. La probabilité de réponse à la chimiothérapie d’un oligodendrogliome de grade 3 est plus grande en présence de codélétion. L’existence de codélétion constitue donc un argument supplémentaire en faveur d’une décision de chimiothérapie, mais l’absence de codélétion ne permet pas d’écarter cette décision. La présence de délétion 1p ou de codélétion est un facteur de bon pronostic pour les oligodendrogliomes et les gliomes mixtes. Ce meilleur pronostic peut s’expliquer par plusieurs facteurs associés à ces deletions : meilleure chimiosensibilité, localisation tumorale préférentiellement frontale, croissance tumorale plus lente et découverte plus précoce.

Losses of chromosomes 1p and 19q are deemed correlated with diagnosis of oligodendroglioma, higher chemosensitivity and better prognosis. We reviewed the literature to evaluate the usefulness of these correlations in daily clinical practice. The rates of deletions relative to histology (WHO classifications) were extracted from 33 studies, including 2666 patients. The 1p deletions and 1p19q codeletion mean rates were respectively 65.4 and 63.3% in oligodendrogliomas, 28.7 and 21.6% in oligoastrocytomas, 13.2 and 7.5% in astrocytomas, 11.6 and 2.9% in glioblastomas. The presence of 1p deletion and 1p19q codeletion were strongly correlated with the histological diagnosis corresponding to oligodendroglioma. Calculation of specificity, sensitivity, predictive positive values and false negative rates suggests that presence of deletion 1p or codeletion represents a strong argument in favor of the diagnosis of oligodendroglioma. However, considering the high false negative rate, absence of such deletions does not rule out the diagnosis. In grade 3 oligodendroglial tumors, the probability of responding to chemotherapy, and the duration of response, were higher when codeletions were present. This suggests that, in these tumors, the presence of codeletion is a strong argument in favor of adjuvant chemotherapy. However, chemotherapy should not be systematically excluded when codeletions are absent, as the chances of response are about 33% in this situation. Data concerning low-grade gliomas were more controversial. Oligodendroglial tumors with 1p deletion or 1p19q codeletion seemed to have a better prognosis, as five-year survival rates were 50% higher than in tumors without deletion. This might be explained by the correlation between 1p deletion and other identified prognosis factors: (1) higher chemosensitivity, (2) tumor location more frequently in the frontal lobe, leading to better resection and lower risk of neurological deficit, (3) slower growth rate, (4) higher risk of epilepsy, leading to an early detection.