Can abscopal effects of local radiotherapy be predicted by modeling T cell trafficking?

The abscopal effect of radiation describes tumor regression in metastases outside of the field upon treatment of one site, and is mediated by radiation-induced anti-tumor T cells. The ability of radiation to generate an in situ tumor vaccine and improve responses to immunotherapy is under intense investigation in the clinic. Preclinical and clinical evidence shows that multiple factors regulate radiation interaction with the immune system within and outside of the irradiated tumor. Poleszczuk and colleagues developed a mathematical model of T cell trafficking between metastases, and in a recent publication propose that the specific metastatic site irradiated determines the ability of T cells to traffic to other metastases and mediate abscopal responses and should dictate clinical decision making [Poleszczuk et al. Cancer Res 76:1009-18, 2016]. Here we critically discuss this model in light of the currently available information about abscopal responses in mice and patients. Caution in relying upon overly simplified models, before validation in real patients, is recommended.