As these categories were primarily based on bulk tumor data, cells co-expressing EGFR and CD44 (classified as GPP cells in this study) may have previously been missed, although single glioma cells have been shown to simultaneously amplify sequence or co-express transcripts for important signaling regulators (Patel et al., 2014; Snuderl et al., 2011). This evidence concerns the gene CD44 and neoplasm.