Immunomodulatory Effects of Radiotherapy

It is well known that radiotherapy, as mainly locoregional treatment, has systemic eff ects as well. The term abscopal eff ect (latin: ab – away from; scopus – target) has been used to describe the regression of distant tumor metastases after completion of primary tumor radiation therapy. It has been shown that radiotherapy can initiate systemic antitumor immunologic response which includes the activation of cytotoxic T-lymphocytes via numerous complex mechanisms. Latest fi ndings indicate that there is an extremely complex interaction between the eff ects of radiotherapy, the activation of diff erent signal pathways, tumor microenvironment and immunologic response. Depending on diff erent tumor and host immune system characteristics, radiation therapy may have either immunostimulatory or immunosuppressive eff ects. Several case reports and smaller studies have described tumor regression after concurrent application of immunotherapy and radiation therapy, mainly in metastatic melanoma, but also in other cancers, such as castration-resistant prostate cancer, breast cancer, non-small cell lung cancer, etc. Many studies researching possible immunomodulatory properties of radiotherapy, as well as the combination of radiotherapy and immunotherapy are currently in progress. Bett er understanding of molecular mechanisms of tumor immunologic regulation and the immunomodulatory eff ects of radiotherapy will open possibilities of creating new more eff ective therapeutic options in treatment of malignant diseases.