Reappraisal of prognostic factors in CNS WHO grade 3 oligodendrogliomas IDH-mutant and 1p/19q co-deleted: Lessons from the French POLA cohort

Background. In the POLA cohort, 3 pathological groups of CNS WHO grade 3 oligodendroglioma IDH-mutant and 1p/19q co-deleted have been described: group 1 (high mitotic count only), group 2 (microvascular proliferation MVP and no necrosis), and group 3 (MVP and necrosis). Methods. 494 patients from the POLA cohort, with a median follow-up of 96 months were included. To identify the impact of the pathological groups and contrast enhancement (CE) in group 1 on overall survival (OS) or progression-free survival (PFS), survival curves were obtained (Kaplan-Meier method) and compared (log-rank test). The prognostic value of clinical factors and CDKN2A homozygous deletion HD were also tested. Multivariate analysis was performed. Results. Survival analysis demonstrated that the pathological groups were associated with both progression-free survival (PFS P = .01) and overall survival (OS P = .001). In group 1, patients with CE (1CE+) had a poorer prognosis compared to those without (OS P = .028, PFS P = .006). Further stratification into group 1CE-, group 1CE+, group 2, and group 3 provided clearer prognostic distinctions (OS P = .002, PFS P < .0001). Other prognostic factors included age (OS P < .0001, PFS P = .002), extent of surgical resection (OS P = .001, PFS P = .003), KPS (OS P < .0001, PFS P = 0.002), postoperative treatment (OS P = .007, PFS P < .0001), and CDKN2A HD (OS and PFS P < .0001). The pathological groups remained of prognostic significance for PFS in multivariate analysis. Conclusions. Necrosis and CDKN2A HD are adverse prognostic factors of WHO grade 3 oligodendrogliomas, IDH-mutant, and 1p/19q co-deleted. Besides, in group 1 patients, lack of CE is a factor of better prognosis.