Early antivascular effects of bevacizumab anti-VEGF monoclonal antibody on colorectal carcinomas assessed with functional CT imaging

Background: The complex effect on anti-VEGF (vascular endothelial growth factor) monoclonal antibodies on the tumor vasculature urges studies to identify the optimal time frames for the administration of such agents with chemotherapy and radiotherapy. Patients and Methods: Using CT scan functional imaging, we examined the perfusion changes of contrast medium induced 7 days following administration of bevacizumab (5 mg/kg iv) in 12 patients with colorectal cancer. Results: CT imaging 7 days after the administration of bevacizumab confinned tumor shrinkage in 3 of 12 cases. The mean Haunsfield units after the injection of contrast medium were significantly lower 7 days following the administration of bevacizumab (P = 0.002). The "perfusion score" significantly decreased after the administration of bevacizumab (P = 0.01). In 5 of 12 cases the perfusion score was by 45% to 75% decreased, in 3 of 12 minor drop of the perfusion score was noted, in 1 of 12 a slight increase was noted, and in 3 of 12 remained unchanged. Conclusion: It is concluded that the antivascular effects of bevacizumab are evident within 7 days from administration in 40% of colorectal carcinomas. The mechanisms by which this early antivascular effect may favor the antitumor efficacy of radiotherapy and chemotherapy require further investigation.