Bevacizumab is a monoclonal antibody medication used to treat a number of different kinds of cancer, including ovarian cancer in patients with recurring disease and glioblastoma. Usually, the treatment response of the drug is initially high, but then subsides in a mechanism that is poorly understood. Bevacizumab functions as an angiogenesis inhibitor that slows the growth of new blood vessels by inhibiting vascular endothelial growth factor A (VEGFA).