'Seed and soil' revisited: mechanisms of site-specific metastasis.

Clinical studies have shown that malignant tumors frequently show definite metastatic patterns. This tendency for neoplasms of a particular histologic type to metastasize to a specific organ is also a characteristic of experimental animal tumor systems. Mechanical entrapment, arrest determined by specific recognition between neoplastic cells and capillaries and organ-determined modulation of tumor growth have all been suggested as mechanisms that regulate this specificity. Experimental evidence for the role that each of these mechanisms plays in the regulation of metastatic patterns of transplantable rodent tumors is discussed in this review.