Methylation Profiling Identifies Stability of Isocitrate Dehydrogenase Mutation Over Time

Area of Science:

• Neuro-oncology
• Molecular Pathology
• Cancer Genomics

Background:

• Isocitrate dehydrogenase (IDH) mutation status is crucial for glioma diagnosis and prognosis.
• IDH mutations are believed to arise early in glioma development and remain constant.
• Recent observations suggest potential loss of IDH mutation status in some recurrent gliomas.

Purpose of the Study:

• To investigate the stability of IDH mutation status throughout glioma evolution.
• To identify and analyze cases with apparent loss of IDH mutation status longitudinally.
• To determine if IDH mutations change during tumor progression or treatment.

Main Methods:

• Retrospective identification of patients with documented IDH mutation status changes (2009-2018).
• Analysis of archived formalin-fixed paraffin-embedded and frozen tissue samples.
• Multi-platform molecular profiling including methylation, copy number variation, Sanger sequencing, ddPCR, and IHC.

Main Results:

• Reviewed 1491 glioma samples, including 78 patients with longitudinal IDH mutant samples.
• All instances of apparent IDH mutation loss were explained by low tumor cell content mixed with non-neoplastic tissue.
• No true loss of IDH mutation status was detected in any patient.

Conclusions:

• IDH mutations are stable throughout glioma treatment and evolution.
• Apparent losses of IDH mutation status are artifacts of sampling and tissue composition.
• Accurate surgical sampling and DNA methylome profiling are vital for reliable glioma diagnosis.