Notably, mutations of TERT promoter (a gene that controls telomeres, small portions of DNA found at the end of each chromosome, which protect the unstable DNA from degradation), have been reported in approximately 75–80% of GBM cases: its role as a prognostic/predictive factor is still uncertain and requires further study [15,16,17,18]. The gene discussed is TERT; the disease is glioblastoma.