PROM1 and acute lymphoblastic leukemia: Although there was a wide range of CD133 expression (measured by the proportion of blasts with detectable CD133) in both MLLr and non-MLLr ALL, mean and median levels of CD133 expression were markedly higher in MLLr cases (Fig. 1b, p < 0.0001, mean 64.9% ± 10.2 s.e.m. vs. 15.7% ± 4.2 s.e.m., median 74.9% vs. 2.5% for MLLr and non-MLLr blasts, respectively; Supplementary Fig. 1f), and a significantly greater number of MLLr ALL samples (9/12) expressed CD133 on the majority of cells (>50%) compared with 4/32 non-MLLr ALL.