Synergistic antitumor activity of immune strategies combined with radiation

Since its discovery more than a hundred years ago, radiation has been used to treat cancer. In recent decades, advances in radiation technology have expanded the role and value of radiation in imaging and treating many forms of cancer. Currently, there is a growing interest in combining radiation with other modalities, such as immunotherapy, to treat a broad range of malignancies. This article reviews the use of standard and novel combinations of radiation therapy and immunotherapy to eradicate tumor cells. The combination of radiation therapy and immunotherapy holds particular promise as a strategy for cancer therapeutics for a variety of reasons. First, there is evidence that immunotherapy is most beneficial when employed early in the disease process and in combination with standard therapies. In addition, radiation may act synergistically with immunotherapy to enhance immune responses, inhibit immunosuppression, and/or alter the phenotype of tumor cells, thus rendering them more susceptible to immune-mediated killing. Finally, as monotherapies, both immunotherapy and radiation may be insufficient to eliminate tumor masses. However, following immunization with a cancer vaccine, the destruction of even a small percentage of tumor cells by radiation could result in cross-priming and presentation of tumor antigens to the immune system, thereby potentiating antitumor responses.