Radiation-induced changes in established tumor immunity.

The effect of radiation therapy on tumor growth and on specific immune resistance to tumor growth was investi gated in mice actively sensitized to a syngeneic sarcoma. While radiation was therapeutic for tumor growth in the radiated field, it was also found that extensive-field radia tion, but not limited-field radiation, could facilitate the growth of tumors in unradiated parts of the animal. The facilitation was greatest with radiation soon after the time of tumor implantation.