Changes in the antitumor resistance of Wistar rats after long-term exposure to radiation in the Chernobyl zone

Antitumor resistance of Wistar rats was studied in terms of dynamic exposure to irradiation in the Chernobyl zone. The antitumor resistance was shown to change in a wave-like manner depending on the duration of exposure: increase (4 mos), restoration of the level which is characteristic of the age control (8 mos), and decrease accompanied by a reduction of the metastasizing rate (16 mos). Based on the dynamics of immunologic indices, characteristics of the growth and metastasizing of tumors induced by transformed cells (A5 cell line), and changes in the phenotypic peculiarities of these cells when growing in control and exposed hosts, a conclusion is made that not only changes in the activity of effectors of anti-tumor resistance but also changes in the rate of in vivo selection of highly metastatic variants of cells exert a considerable effect on the course of the tumor process in prolonged exposure to combined irradiation.