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To assess the effect of chemotherapy plus bevacizumab on tumor vessels, as well as the reversibility of this effect, using contrast-enhanced ultrasonography (CEUS) and histology in patients with metastatic liver tumors derived from colorectal cancer.The study included 12 patients who received chemotherapy plus bevacizumab, experienced a reduction in tumor vascularity as demonstrated by CEUS and consequently underwent liver resection. CEUS was performed before and after four courses of chemotherapy and before surgery. The numbers of microvessels highlighted by anti-CD34 antibodies in the viable tumor tissue were counted to quantify the microvessel density (MVD). As a control, 12 surgical specimens from 12 patients who had not received chemotherapy were examined.A reversal of tumor vascularity was observed in 10 of 12 patients. In two patients, the vascularity remained reduced. The MVD in the treatment group was significantly lower than that observed in the group without treatment.The data suggest that the tumor vessels regenerated substantially, although the effect of chemotherapy plus bevacizumab remained weak for approximately 6 weeks after the cessation of treatment. Therefore, future research must determine whether bevacizumab should be used prior to surgery. J. Surg. Oncol. 2013;107:155–159. © 2012 Wiley Periodicals, Inc.