The systemic immunostimulatory effects of radiation therapy producing overall tumor control through the abscopal effect

Abstract

Objective: Emerging studies show that radiation therapy produces an important out of field (distant) effect known as the ‘‘abscopal effect” in nonirradiated tumor sites. The objective of this study was to provide an overview of the current state of knowledge and clinical experience of radiation therapy producing abscopal effects in the management of different types of malignant diseases. Methods: Peer-reviewed published clinical evidence on the abscopal effect of radiation therapy was collected using electronic databases such as Medline via PubMed and Google Scholar. The reference lists were searched in the publications that we obtained in an attempt to find additional relevant publications. Non-indexed peer-reviewed journals were manually searched and relevant information was extracted. The search was restricted to English language articles. The clinical data on the abscopal effect of radiation therapy were reviewed and the outcomes have been summarized. Results: Currently, only clinical case reports and anecdotes have slowly converted into solid clinical data and interest is building in the field of radiation therapy, specifically on how local radiation can produce the abscopal effects for the management of different types of malignant tumors. Extensive clinical evidence suggests that the radiation therapy induced abscopal antitumor effects are mediated by immune cells such as the T-lymphocytes. This forms a basis for using radiation therapy in combination with immunotherapy to augment the abscopal response rates in cancer patients. Current evidence demonstrates that radiation therapy induces abscopal responses across many tumor types. Conclusion: Together, the clinical outcomes from published reports suggest that localized radiation therapy is capable of inducing abscopal effects in a wide variety of malignant tumors. With the advent of novel immunotherapies, the potential for immune activation by radiation defines a novel role for radiation therapy in the treatment of systemic disease. A clinical consideration of the abscopal effects produced by radiation therapy could lead to a revolutionary change in the current management of patients including radiation treatment strategies and immunotherapies for various malignant tumors.