BMI1 and cancer: Given that the GSC state is not a stable clonal subpopulation but rather a plastic state induced by the tumor microenvironment, we scored cells based on classic GSC markers (PROM1, SOX2, NES, OLIG2, BMI1, NANOG, POU5F1) and defined the top 2% of cancer cells with the highest stemness scores as GSCs (Figure 1D-E).