Analysis of the lodgement and extravasation of tumor cells in experimental models of hematogenous metastasis.

This review summarizes our experiments on the metastatic distribution patterns of Yoshida sarcoma and several strains of rat ascites hepatomas. These dissemination patterns cannot be explained entirely by either anatomical-mechanical considerations or by the seed-and-soil hypotheses for metastatic localization. In some experimental situations, anatomical-mechanical factors seem more important, but in others the seed-and-soil hypothesis offers a more compelling interpretation. Lodgement of tumor cells in the microcirculation of different organ vascular beds can occur by three non-exclusive mechanisms: direct attachment to vascular endothelial cells; direct adhesion to exposed vascular basement membrane components or by entrapment in thrombi. Similarly, extravasation can also occur via several mechanisms. The first, involves infiltration of tumor cells into perivascular tissues via their own movement. A second mechanism involves sequestration of tumor cells beneath vascular endothelial cells where they are separated from the blood stream. The third option for extravasation involves 'explosive' displacement in which the blood vessel wall swells as a result of intracapillary growth of tumor emboli causing the vessel to rupture.