Experimental liver metastatic model using MKN74 cells. (A) Morphological analysis of liver metastatic foci of DDR1-silenced and control MKN74 cells. Left, mean tumor number; right, mean tumor volume. (B) Representative image of implanted splenic tumor and liver metastatic foci at 42 days after implantation. It was visually confirmed that there were many liver metastatic foci in control livers, while in the shDDR1 group, there were no metastatic lesions in the liver in spite of observed splenic engraftment. Yellow circle: primary splenic tumor. Yellow arrow head: liver metastasis. (C) Immunohistochemical analysis of liver metastasis. One week after implantation, micrometastatic lesions were detected by hematoxylin and eosin staining in both control and shDDR1 implanted tumors. Six weeks after implantation, liver metastasis was enlarged in control tumors (black arrow), while no liver metastatic foci were observed in shDDR1 implanted tumors. Several GFP-positive solitary cells were observed in the vessels however. (D) CD31 immunofluorescent staining of micrometastatic foci at 1 week after splenic implantation in each group. Right, mean microvessel area in each group. Microvessel area was significantly reduced in DDR1-silenced micrometastatic foci. Data are expressed as means ± SEM. **P < .01.