PROM1 and glioblastoma: McCord et al. observed that CD133+ glioblastoma stem-like cells were sensitive to irradiation compared with current established cell lines (most established cells are CD133 negative).47 Dittfeld et al. found that CD133 expressing cells did not identify radioresistant subpopulations in colorectal cancer cells HCT116.48 Thus, although many previous studies reported fractionated small dose irradiation (usually < 5 Gy/fraction) resulted in accumulation of marker identified resistant stem-like cells that may give rise to tumor recurrence and metastases, these results are not consistently observed.