Alternative Lengthening of Telomeres (ALT) is seen in a proportion of oligodendrogliomas and is associated with a worse prognosis

Summary

Oligodendrogliomas are known to be mutated for TERTp, and in this report, we evaluated 112 IDH-mutant, 1p19q codeleted oligodendrogliomas for ALT by FISH, and FISH for copy number changes of CDKN2A, MYC, PDGFRA, EGFR, chromosomes +7/10 and TERT-rearrangement. Enigmatically, 35.7% of cases were ALT-positive in spite of the vast majority of them being TERTp-mutant. ALT was associated with a shorter PFS (p=0.009) and remained an independent prognosticator in multivariate analysis. ALT was also associated with MYC amplification. ALT-positive cases were further examined with targeted sequencing. No genes were found to be of prognostic significance in this group.