Antitumor abscopal effects in mice induced by normal tissue irradiation using pulsed streamer discharge plasma

Abstract

An antitumor abscopal effect is occasionally observed in radiotherapy and plasma treatment. It is a remote antitumor effect induced by tumor irradiation that delays the growth of other distant, nonirradiated tumors. In this study, it was demonstrated that the plasma irradiation of normal tissues (not tumors) also leads to an abscopal effect. When a pulsed streamer discharge was irradiated to the left flanks of mice where no tumor existed, the growth of murine colorectal carcinoma CT26 tumors in their right limbs was delayed. This abscopal effect was significant for mice with small tumors before plasma irradiation, whereas it was not significant for those with large tumors before plasma irradiation. The abscopal effect induced by normal tissue irradiation was compared to the antitumor effect induced by direct tumor irradiation. Contrary to our expectation, normal tissue irradiation delayed the tumor growth equally or more than the direct tumor irradiation under the present experimental conditions.