Although many studies have demonstrated intercellular genomic heterogeneity as a fundamental feature of diffuse glioma and other solid cancer progressions,19,20,22,25,35,42 IDH mutation is considered to be an early oncogenic event initiating glioma evolution,4,40,43–45 and as such is generally found with high penetrance across the tumor cell population of a given glioma. The gene discussed is IDH1; the disease is central nervous system cancer.