Effect of wide field irradiation on unirradiated tumors in the same host

The immune system is believed to influence tumor growth; and, ionizing radiation has an immunosuppressive potential. However, investigators have come to conflicting conclusions regarding the effect of localized radiation therapy on both the immune system and on distant tumor growth. This report describes two murine models. In the first, B-16 malignant melanoma was implanted simultaneously into the left groin and right axilla. In the second model, in order to immunize the mouse, B-16 melanoma was implanted into the left groin 1 week before implanting melanoma into the right axilla. In both models, 600 rad caudal hemibody irradiation was given in a single fraction with a 4 MeV linear accelerator. Significant decrease in the growth of irradiated groin tumors occurred. Unirradiated axillary tumors did not demonstrate increased growth. We conclude that, at least in these models, high dose, wide-field irradiation does not augment the growth of unirradiated tumors in the same host.