A Systematic Review on the Impact of Hypofractionated and Stereotactic Radiotherapy on Immune Cell Subpopulations in Cancer Patients

SIMPLE SUMMARY: The role of different radiotherapy fractionation on immune cells is yet to be determined. Monitoring immune cells and understanding their quantity and quality changes during and after radiotherapy could have relevant implications on the development of novel therapeutic strategies. The aim of our review was to analyze the evidence of the literature regarding radiation-induced changes in immune cells in patients undergoing stereotactic body radiation therapy or hypofractionated radiation therapy and assess their potential impact on future combined systemic therapies. Preliminary studies seem to confirm a strong modification of the tumor immune environment and peripheral immune cell landscape after hypofractionated and stereotactic regimens. ABSTRACT: We investigated how hypofractionated radiotherapy (HFRT) and stereotactic body radiotherapy (SBRT) may impact immune cells in different type of tumors. A systematic review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The PubMed, Embase and Cochrane databases were searched. Overall, 11 studies met the inclusion criteria and were eligible for the present analysis. Both HFRT and SBRT have different impact on lymphocyte subpopulations, confirming their immunomodulatory effect which may have a crucial role in future combined treatment with new emergent therapies such as immunotherapy. Further studies are needed to shed more light on this emerging topic to ultimately improve patient care, treatment and clinical benefits for cancer patients.