RYR1 and glioblastoma: Our previous analysis of CcO activity in GBM biopsies from patients subjected to TMZ-radiotherapy [6], [7] demonstrated that the CcO activity in recurrent tumors is significantly greater than the activity in primary tumors, suggesting that during tumor regrowth, a switch from glycolytic (low CcO activity) to OXPHOS metabolism (high CcO activity) may occur.