Tumor cells also may escape from drug sensitivity by exposure to growth factors usually secreted by the neighboring stromal cells, which is well accepted as environment-mediated drug resistance (Figure 2B).93 Early clinical trials have observed that tumor vasculature in GBM patients may be normalized by VEGF inhibitors; however, this was reversible after a 1-month treatment. The gene discussed is VEGFA; the disease is glioblastoma.