The probability of influence of the abscopal effect on reduction of similar far away 4T1 cell line tumors by irradiation of main tumor

Abstract

The most important problem with radiotherapy is the limitation of whole body irradiation of a metastatic patient. There are evidence showing that similar effect will occur in non-irradiated tumors similar to the irradiated ones. This effect is called abscopal effect. In the present study, the abscopal effect on local induced mice breast cancers has been investigated. One million of 4T1 mice breast cancer cell line was injected to balb/c mice subcutaneously while being under anesthesia. After the growth of tumors till becoming palpable, one of two induced tumors were exposed to total 28 Gy, with gamma rays emitted from a cobalt -60 tele-therapy machine in 14 fractions with 2 Gy daily doses. Tumor volumes were measured, using the caliper. The data was analyzed by the use of non-parametrical and ANOVA tests. Similar growth in non-irradiated control tumors was seen. After 10 or 11 fractions of one- side irradiation and total dose of 20 to 22 Gy, however, non-irradiated tumors, similar to irradiated ones, showed similar effect, reduction of size and volume different from control groups (P<0.05).The reduction of non-irradiated tumors relative to irradiation of another tumor in the same mouse is the emblem of occurrence of the abscopal effect. The mechanism of the abscopal effect is unknown but it could be related to the release of cytokines from irradiated tumors with their receptors existing on the surface of non-irradiated tumors. By induction of this effect, the remission probability of small metastases after local irradiation could be possible.