Combination of radiotherapy and immune treatment: First clinical data.

There is a very strong biological and pre-clinical rationale for combining radiotherapy with immune treatment. Radiation affects all steps in the immune response to antigens and clearly upregulates key-molecules on the cancer cell and in the tumor micro-environment, such as MHC class I antigens, tumor-associated antigens and the creation of neo-antigens as well. In many pre-clinical models, radiation together with the right combination and timing of immune therapy leads to regression of distant metastases, at remote non-irradiated sites of the body, the so-called "abscopal effects". The combination generally also increases the local tumor control. Although a plethora of clinical trials are ongoing or are being planned, clinical data are sparse and mostly even retrospective. The few published prospective studies nevertheless support a synergy between radiotherapy and immune treatment. At least with checkpoint inhibitors, the side effects of the combined modality treatment do not seem to be significantly higher than of each modality alone. In the coming years, more solid data will surely appear and it is anticipated that radiotherapy will become an integral part of immune therapy.