[Cancer metastasis and blood vessels]

The ultrastructural features on interaction of tumor cells and blood vessels in the process of hematogenous metastasis formation by Yoshida sarcoma, 5 strains of Yoshida rat ascites hepatoma, murine B16 melanoma variant sublines, and others have been described and illustrated. Intravasation and extravasation of tumor cells appeared to be similar cell biological phenomenon, in which two different ways were involved: 1) tumor cells migrated through the pores in the vascular walls which were produced by direct actions of tumor cells, and 2) endothelial cell cytoplasms enclosed the tumor cells neighboring to the vascular walls and as a result intravascular or extravascular tumor cell movement occurred. Tumor cells arrested in a target organ were in close contact with vascular endothelial cells and further with basement membrane when the endothelial linings were removed. In some regions we found junction-like structures between these cells. This appeared to be corresponding to the lodgement of tumor cells in the target organ. Extravasated tumor cells produced three different features of metastatic lesions in the combination of tumor strain and the organ affected; formation of tumor nodules accompanying neovasculature, spreading of tumor cells along the perivascular tissue of an organ, and diffuse infiltration of tumor cells in an organ. It has been discussed that these features in every process mentioned above are determined by specific interaction of tumor cells and host cellular components, especially blood vessels including tumor neovasculature.