Analysis of the clinical impact of the diagnostic reclassification of brain gliomas according to the World Health Organization classification (2016)

Introduction. Since the introduction of genetic and molecular criteria in the 2016 World Health Organization (WHO) classification of brain tumours, there has been a diagnostic reclassification between certain astrocytomas and oligodendrogliomas with histological and genetic discordances, the prognosis of which is unknown. Aim. To analyse the implications of the diagnostic reclassification of brain gliomas according to the 2016 WHO criteria, especially depending on isocitrate dehydrogenase (IDH) mutation and 1p19q codeletion. Patients and methods. We conducted a retrospective study of gliomas treated from 1 January 2012 to 31 December 2016, with analyses of clinicoradiological aspects and prognoses, and with available and complete follow-up until 31 March 2019. Results. From a total of 147 brain gliomas, a molecular diagnosis and a diagnostic re-evaluation were carried out in 69 cases (grade II-1V astrocytomas or oligodendrogliomas). Twenty-four reclassified gliomas were detected, usually oligodendrogliomas that became astrocytomas, and which showed greater survival, derived from their not being classified as grade IV. The reclassified gliomas, all grades II/III, mostly began with seizures, without focus, with single lesions, < 17 cm(3) and with oedema, although with similar survival rates. The prognostic factors were: young age, focus, grade II and no contrast enhancement or necrosis, or multiplicity. No variations were detected according to the molecular pattern with IDH mutation or codeletion. Conclusion. The changes in diagnosis after the WHO classification of 2016 present specific clinical-radiological characteristics in this series, but no greater survival, although, due to the habitual survival in these cases, they would require a longer follow-up time.