EGFR and glioblastoma: In our study, TMZ clearly activated many EGFR downstream signaling pathways, including those of p38, JNK, and AP-1, shown by others53,55,56, however, basal MMP9 expression levels were below the detection limit in most GBM cells, as shown in Fig. 2C. Nature of low basal MMP9 level in GBM cells can result in extremely difficult technical issues.