Together, these data suggest that, since the rate of MGMT promoter methylation drops sharply below a TERT promoter VAF of ~ 0.18 (i.e., ~ 35–40% tumor cellularity) for IDHwt GBM, cases with such low VAF may be at increased risk of false-negative MGMT promoter methylation results by pyrosequencing. The gene discussed is TERT; the disease is glioblastoma.