Radiation induced abscopal antitumor effect

Radiation therapy is a cancer treatment that causes direct death of cancer cells, however there is a number of reports on anticancer effect of radiotherapy, that may be considered as tumor regression at sites that are outside the irradiated volume, this phenomenon was called as abscopal antitumor effect. The article presents results of the model study of the abscopal antitumor effect. The model of very aggressive ascitic mammary tumor “Ehrlich ascites carcinoma” (EAC) was used for the study. First, one-step bilateral grafting of EAC cells to mice hind extremities was performed, the following step was the formation of tumor contralateral nodes in the hips. In 5 days after the cells transplantation, the right (target) node was locally irradiated with 60Co gamma rays with a dose of 30 Gy. The growth of the left (non-target) and the target tumor nodes was watched during 20 days after irradiation. It was found that local irradiation of the right tumor node with a dose of 30 Gy at an early stage of tumor growth caused inhibition of the left, non-target tumor node growth from 10 to 49% relative to the growth of the tumor nodes in the control group of the tumor bearing mice. In order to reduce the dose burden in this model, the impact of fractionated irradiation with single dose of 10 Gy, to a total dose of 30 Gy on the abscopal effect was studied. The ability of the immune system of the mice with transplanted tumors in both hips and the irradiated target tumor node to respond to an antigenic stimulus was studied. The study results are the following: the immune system of mice, with a transected tumor in both thighs and subsequent gamma-ray irradiation of the target tumor node at a dose of 30 Gy respond to the antigenic stimulus; radiation doses to the target tumor node are crucial in achieving the abscopal effect; the use of complementary therapeutic methods, such as targeted therapy or immunotherapy, will increase the probability of the abscopal effect achieving.