Studies on rat mammary adenocarcinomas: a model for metastasis.

Studies carried out by the authors on the rat mammary adenocarcinoma cell lines MAT 13762 and DMBA-8 are summarized. A series of variants and somatic cell hybrids have been prepared and partially characterized in terms of phenotypic properties which may correlate with metastatic potential. These include measurement of in vitro migration, lectin binding properties, expression of procoagulant activity and shedding of cell surface components. Particular emphasis has been placed on the production of enzymically-active plasminogen activator, as this seems to correlate with the ability of cells to metastasize. The finding has also been made that several of the cell types studied produce, in vitro, an inhibitor of plasminogen activator which may influence the metastatic behaviour of tumor cells. Results obtained are discussed in the context of the usefulness of these tumor systems for the study of spontaneous and experimental metastasis and the factors involved in these processes. Preliminary results of cloning and fluctuation analysis of metastatic potential together with discussion of the role of the metastatic heterogeneity and the formation of metastatic variants by mutation events are included.