We found that 89.2% of the quiescent mCherry+/mVenus+ cells co-expressed SOX2 (Supplementary Fig. 8e, f) and that 95.2% of mCherry+/mVenus+ cells were negative for proliferation marker Ki67 (Fig. 5f, g) confirming the visualization of slow-cycling/quiescent cells in brain cancer organoids. Here, MKI67 is linked to brain cancer.