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 exposur e to irradiation in the Chernobyl zone. The antitumor resistance was shown to change in a wave-like manner depending on the duration of exposure: incr ease (4 mos), restoration of the level which is characteristic of the age c ontrol (8 mos), and decrease accompanied by a reduction of the metastasizin g rate (16 mos). Based on the dynamics of immunologic indices, characterist ics 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 on ly changes in the activity of effectors of anti-tumor resistance but also c hanges in the rate of in vivo selection of highly metastatic variants of ce lls exert a considerable effect on the course of the tumor process in prolo nged exposure to combined irradiation.