Artificial metastases and decrease of fibrinolysis in the nude mouse lung after hemithoracic irradiation.

X-irradiation to the nude mouse lung and the ensuing pulmonary metastasis of the injected human cancer cells were investigated. Human cancer cells were injected intravenously into nude mice following 20 Gy right hemithoracic irradiation. The right lungs showed evidence of metastasis while metastasis was slight in the non-irradiated left lung. Platelet aggregation and fibrin deposition occurred around the arrested cancer cells in the capillaries of the right lung. The fibrinolytic activity of the irradiated right lung was lower than that of the non-irradiated contralateral lung. Natural killer cell activity was lower in the right-lung-irradiated mice than in the non-irradiated mice. We conclude that when the target organ is exposed to X-irradiation, there will be a decrease in fibrinolytic activity, a condition paving the way toward a metastasis.