Increased metastatic capacity of Lewis lung tumor cells by in vivo selection procedure.

Lewis lung tumor cells from liver metastases originally obtained from an intrasplenic tumor, and lung metastases obtained from an intramuscular transplant, were repeatedly passaged in the corresponding transplantation sites (spleen, intramuscular). Cells from liver metastases injected into the spleen gained an increased metastatic capacity. The same phenomenon was observed with lung metastatic cells injected intramuscularly, but to a lesser degree. In all passages metastases occurred only in the organs receiving the venous blood from the primary site. The enhanced metastasis formation may be a result of a selection of tumor cells resistant to host cytotoxic cells and/or of selection of tumor cells 'seeding' successfully in target organs.