Changes of intratumoral microvessels and blood perfusion during establishment of hepatic metastases in mice.

PURPOSE To prospectively evaluate the stepwise changes that occur in intratumoral microvessels and microcirculation during the establishment of murine colonic hepatic metastases by using in vivo fluorescent microscopy and to compare the changes with tumor angiogenesis evaluated with an immunohistochemical study. MATERIALS AND METHODS This study was approved by the institutional animal care and use committee. Twenty-five mice with hepatic metastases created with injection of murine colonic adenocarcinoma (colon 26) tumor cells into the spleen were examined with in vivo microscopy and immunohistochemical study for CD34, intracellular adhesion molecule (ICAM-1), and alpha smooth muscle actin (alpha-SMA). The tumor size, microcirculation in tumors, intratumoral microvessel density (MVD), afferent MVD, and CD34-positive MVD were evaluated. The data among the tumors that showed different hemodynamic or immunohistochemical patterns were compared with the Kruskal-Wallis test and the Student t test. RESULTS Four stepwise patterns were observed according to the changes in morphology, hemodynamics, and immunohistochemical characteristics of intratumoral microvessels during the establishment of hepatic metastases, as follows: metastases without definite intratumoral blood perfusion or any intratumoral microvessels (mean diameter, approximately 180 microm), metastases with portal perfusion and intratumoral ICAM-1-positive residual hepatic sinusoids (mean diameter, approximately 290 microm), metastases with mixed portal and arterial perfusion and increased CD34-positive microvessels and alpha-SMA-positive arterioles (mean diameter, approximately 520 microm), and metastases with exclusively arterial perfusion and increased CD34-positive microvessels and alpha-SMA-positive arterioles (mean diameter, >2000 microm). The differences among the mean sizes of the tumors that showed these four patterns were statistically significant (P < .01). CONCLUSION Stepwise changes of intratumoral microcirculation were revealed from direct diffusion, to portal perfusion, to mixed portal and arterial perfusion, and finally to arterial perfusion in accordance with stepwise tumor neovascularization during the growth of murine colonic hepatic metastases.