533P - Oligodendrogliomas: What is the impact after the introduction of the WHO molecular classification?

Background

Oligodendrogliomas are rare tumors and affect young people. In 2016, the new WHO classification was introduced that includes molecular features (IDH mutation and 1p/19q codeletion) that were not present in previous classifications. Currently, there is no data indicating the impact of this new classification on our clinical practice. The objective of this study is to review the clinical evolution of a cohort of patients, before and after reclassification, using molecular criteria.

Methods

Cases with a diagnosis of grade 2 and grade 3 oligodendroglioma and oligoastrocytoma were identified in the registries of two tertiary hospitals. A total of 182 cases, corresponding to a period of 37 years (between 1977 and 2014), were identified and termed initial cohort. Subsequently, IDH mutation and codeletion of 1p/19q analysis were performed in this cohort. A total of 91 patients fulfilled these characteristics and were termed the reclassified cohort. The clinical evolution of both cohorts was analyzed.

Results

The mean age of the cohort was 45 years (14-75), with a Males: Female ratio of 61%/39%. Frontal lobe location 60%, 65% grade 2 and 22% oligoastrocytomas. Complete resection 47% (subtotal 22%, partial 20%, biopsy 7%). After surgery, 50% received radiotherapy, 30% chemotherapy, 36% did not receive adjuvant therapy. The median follow-up was 9 years. Unlike what was observed in the initial cohort, there were no statistical differences in median overall survival (OS) in the reclassified cohort regardless of grade; grade 2, 13.3y (95%CI 8.2-18.4), grade3, 12 years (95%CI 5.6-18.3), therefore, grade loses its prognostic impact with the new molecular classification. OS in the excluded cohort was 7.52years (95%CI 4.67-10.38). The OS in those cases without adjuvant treatment was 12 years. 30% of oligoastrocytomas in the initial cohort were reclassified to oligos.

Conclusions

Molecular classification allows a more accurate selection of oligodendrogliomas and implies that cases have a better prognosis, regardless of grade and treatment received. These data should be taken into account in clinical practice for a better selection of the risks and benefits of adjuvant treatment.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

M.A. Vaz Salgado: Financial Interests, Personal, Advisory Board: Novocure; Financial Interests, Personal and Institutional, Coordinating PI: Pfizer. J.M. Sepulveda Sanchez: Financial Interests, Personal, Invited Speaker: GSK; Financial Interests, Personal, Advisory Board: MSD, Novocure, CeCaVa, Cantex; Financial Interests, Personal and Institutional, Research Grant: Pfizer, Cantex. L.L. Ley: Non-Financial Interests, Member, President: Sociedad Española de Neurocirugía; Non-Financial Interests, Member: Grupo Español de Investigaciones Neurooncológicas. A. Carrato Mena: Financial Interests, Personal and Institutional, Advisory Board: Pfizer, Bayer, Merck, MSD, Novartis, Shire. All other authors have declared no conflicts of interest.