Oligodendrogliomas: findings after classifying the same cohort using pre- and post-World Health Organization (WHO) 2021 criteria.

The 2021 World Health Organization (WHO) classification includes the presence of isocitrate dehydrogenase (IDH) mutation and 1p/19q codeletion for oligodendrogliomas. The objective of this study was to evaluate the impact of the introduction of this classification in a cohort of oligodendrogliomas. A total of 182 cases with an initial diagnosis of oligodendroglioma by histological criteria were identified, including Grades 2 and 3 and oligoastrocytoma (initial cohort). Subsequently, IDH mutation and 1p/19q codeletion were determined and were present in a total of 91 cases (reclassified cohort). The clinical evolution of both cohorts was analyzed. The mean age was 45 years (14-75), 65% were Grade 2 and 22% were oligoastrocytomas. Complete resection was performed in 47% and biopsy in 7%. After surgery, 50% received radiotherapy, 30% chemotherapy and 36% did not receive adjuvant therapy. In the reclassified cohort, there were no statistically significant differences between Grade 2 and Grade 3 oligodendrogliomas, the median overall survival (OS) in Grade 2 was 13.3 years [95% confidence interval (CI) 8.2-18.4] and 12 years in Grade 3 (95% CI 5.6-18.3). However, in the initial cohort, significant differences were found according to tumour grade. Even in cases without adjuvant treatment, the median OS was 12 years. Compared with this data, the median OS for the cohort that did not meet IDH mutation and 1p/19q codeletion criteria was 7.52 years (95% CI 4.67-10.38). Molecular classification allows a more accurate selection of oligodendrogliomas and implies cases with a better prognosis, regardless of the grade and treatment received. These data should be taken into account in clinical practice and clinical trials.