As early as the 20^th century, it has been observed that radiotherapy (RT), as a local therapy, can activate the adaptive immune system, resulting in spontaneous regression of tumors out of the radiation field, which is known as "abscopal effect". Although the occurrence of abscopal effect is still rare, with the gradual increase in the application of immunotherapy, more and more clinical cases of abscopal effect have been reported. Increasing attention has been paid to the therapeutic potential of RT in inducing systemic anti-tumor response. Especially, the combination of RT and immunotherapy enhances the research value of abscopal effect. However, its mechanism has not been fully elucidated, and the optimal timing, dose and fractionation of RT are also under study. How to classify the beneficiary groups is also a key issue. In this article, the history of abscopal effect, and the role of RT and immunotherapy in this phenomenon were briefly introduced, and the existing controversies in clinical application were illustrated, aiming to clarify the direction of current research and development and open a new chapter for tumor treatment in a short period of time.

Radiotherapy; Abscopal effect; Immunotherapy; Immunosuppressive microenvironment