Vascular endothelial growth factors (VEGF) are key mediators in tumor growth and angiogenesis. Suppression of tumor growth by VEGF-blockade therapy is a popular approach towards improving cancer treatment. Bevacizumab (BV) is monoclonal antibody used to inhibit VEGF that has shown promise in treating several forms of cancer. However, BV is ineffective in certain forms of cancer, presumably due to unpredicted compensatory mechanisms of VEGF deficient tumors. In clinical practice, it would be advantageous to determine as early as possible whether a particular cancer would be responsive to BV treatment. In this study, we evaluate the vascular response (perfusion and molecular expression) of two human cancer cell lines (SKNEP and NGP) implanted in mice to BV therapy using high-frequency ultrasound imaging. Size-selected, lipid-coated microbubbles were used as vascular probes.