Differences in blood vessel morphology between tumor periphery and center. A: Formalin fixed liver sections with CRC liver metastases were stained with antibodies to CD34 (staining of endothelial cells on immature vessels). Scale bar=200μm. Inset 1 depicts tumor vessels (arrows) in the tumor center staining strongly for the CD34 endothelial marker. Inset 2 depicts tumor vessels (arrows) in the tumor periphery staining weakly for the CD34. Inset 3 depicts host vessels (arrows) being co-opted by the tumor displaying weak or no CD34 staining. B: Quantification of CD34 positive vessels in tumor center and tumor periphery expressed as CD34 positive vessels /mm2. Black bars = tumor periphery, Grey bars = tumor center. Significantly more CD34 positive vessels are seen in the tumor center (*P<0.001). Quantification of αSMA pericyte association with tumor vessels revealed a significantly greater number in the tumor periphery compared to the tumor center (* P<0.0001, Black bars = tumor periphery, Grey bars = tumor center. Data is expressed as mean value± SEM, with n≥5 for each group. Data was not normally distributed and non-parametric analysis was performed and statistical significance determined using Kruskal Wallis and Mann-Whitney U test.