Colocalization analysis revealed that 48% of ASCL1+ tumor cells were positive for the proliferation marker Ki67 (Figure 1k–m,o), whereas over 90% of ASCL1+ cells were OLIG2+ and SOX2+ (Figure 1o), indicating that these three transcription factors are coexpressed in the majority of the PDX‐GBM cells in vivo. The gene discussed is SOX2; the disease is glioblastoma.