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Study Objectives: To establish a clinically relevant animal model of pulmonary metastases of human non-small cell lung carcinoma (NSCLC) cells in severe combined immunodeficiency (SCID) mice, which can be used for repetitive investigations, so as to improve our understanding and management of the cellular and molecular mechanisms of human lung cancer metastases.Methods and Results: SCID mice subcutaneously injected in the flank with 1 x 10(6) EBC-1 cells derived from human lung squamous cell carcinoma were killed weekly for examination until 12 weeks after tumor inoculation. The biological characteristics of implanted tumors and their metastatic foci were investigated by hematoxylin-eosin staining and immunostaining for neutrophil elastase (NE). Three weeks after ectopic implantation, EBC-1 cell lines formed a tumor at the inoculation site and grew steadily to show a plateau at 10 weeks. EBC-1 cells formed multiple metastases in the lung 7 weeks after tumor inoculation; their numbers increased steadily until 12 weeks in all mice. Immunoreactivity for NE was intense in the metastatic tumor cells. Then, to establish the primary tumor amputation/pulmonary metastasis model and to evaluate how primary tumor amputation influences the development of pulmonary metastases at the cellular and molecular level, excision was performed before (3 weeks and 5 weeks after inoculation) and after (7 weeks and 9 weeks after inoculation) formation of lung metastases. When the primary tumor was excised 3 weeks after tumor inoculation, all mice had pulmonary metastasis at 12 weeks after inoculation. Blood samples obtained at 3 weeks after tumor inoculation contained human beta-actin messenger RNA, which represents circulating tumor cells.Conclusion: Our NSCLC EBC-1 pulmonary metastasis model is reliable, technically simple, and predictably results in pulmonary metastasis from early hematogenous spread. This model may be useful for elucidating the mechanism of pulmonary metastasis in human lung cancer, and testing anti-metastatic efficacy of therapeutic agents in vivo. [ABSTRACT FROM AUTHOR]