Bevacizumab, marketed under the brand name Avastin, is a monoclonal antibody used to treat various types of cancer. Developed by Genentech/Roche, this drug works by inhibiting the activity of vascular endothelial growth factor (VEGF), a protein that stimulates new blood vessel formation (angiogenesis). By blocking VEGF, bevacizumab helps to starve tumors of the blood supply they need to grow.