Radiation to the chest at the time of amputation of a transplantable rat hepatoma growing in the leg is an effective means of preventing or arresting metastatic pulmonary lesions. In these experiments 3 out of 20 rats treated by surgery alone were cured of tumors, whereas 11 out of 20 rats treated by surgery and radiation of the lungs were cured. Serum concentrations of α1-fetoprotein (AFP) were used to monitor the presence of viable tumors in each animal, providing a method of detecting metastases when they would not otherwise have been found. The mechanism of the effect of radiation to the lungs in suppressing metastases is not clear at this time. Although a direct killing effect on tumor cells present in the lung after amputation of the primary site of growth is most likely, the apparent regrowth and remission in three irradiated rats as revealed by normalization of elevated serum AFP concentrations suggest an active response of the host in some instances.

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