EGFR and glioblastoma: The effect of erlotinib on GBM cells cultured on the hydrogel was dependent on the EGFR mutation. Erlotinib had no cytotoxic effect in EGFRvIII cells. However, cells with EGFR + were only susceptible to the drug in the absence of HA, suggesting that HA promotes the inhibition of this receptor by deactivating STAT3.