Incubation of AMG 595 with U251 cells expressing EGFRvIII led to potent growth inhibition. AMG 595 treatment induced significant tumor mitotic arrest, as measured by phospho-histone H3, in GBM subcutaneous xenografts expressing EGFRvIII….These results demonstrate that AMG 595 is a promising candidate to evaluate in EGFRvIII-expressing GBM patients.