PTTG1 and glioblastoma: Interestingly, previous studies showed that glioma PDOs allowed to grow larger developed hypoxia gradients, which is a hallmark of GBM.[23, 39] Thus, these findings suggest that there probably exists a loop mechanism between CDC20+KIF20A+PTTG1+ cell subpopulation and hypoxia core activation, leading to the glioma progression.