Immuno-radiotherapy: A review of the rationale, recent clinical developments and future prospects

Thanks to the success of checkpoint inhibitors, immunotherapy now plays a major role in the management of a large number of solid tumors, while the number of indications continues to grow and new combinations could, in the near future, further modify treatment standards. However, the response rates of immunotherapies as monotherapy are modest and their use is increasingly considered in combination with other cancer treatments (chemotherapy, surgery, radiotherapy or certain targeted therapies). Combinations with radiotherapy seem particularly attractive because there is a strong experimental rationale linking part of the efficacy of ionizing radiation to an induced stimulation of both of the innate and adaptive response. Many early phases and a number of large randomized combination trials have published efficacy and safety results, while important trials are still ongoing and will provide answers in the near future. This short review recalls the experimental biological rationale for immuno-radiotherapy and highlights some of the fundamental directions being explored, then presents the clinical efficacy and safety results available to date, those expected in the near future, and finally outlines the outlook in this rapidly evolving field.