Combinatorial approach of immuno-proton therapy in cancer: Rationale and potential impact

Cancer management is an expansive, growing, and evolving field. In the last decade or so, immunotherapy (IT) and particle beam therapy have made a tremendous impact in this domain. IT has already established itself as the fourth pillar of oncology. Recent emphasis has been centred around combination therapy, postulating additive or multiplicative effects of combining IT with one or more of the three conventional "pillars," that is, surgery, chemotherapy, and radiotherapy. Radio-IT is being increasingly explored and has shown promising outcomes in both preclinical and clinical settings. Particle beam therapy such as protons, when used as the radiotherapeutic modality in conjunction with IT, can potentially limit toxicities and improve this synergism further. Modern proton therapy has demonstrated a reduction in integral dose of radiation and radiation-induced lymphopenia in various sites. Protons, by virtue of their inherent clinically desirable physical and biological characteristics, namely, high linear energy transfer, relative biological effectiveness of range 1.1-1.6, and proven anti-metastatic and immunogenic potential in preclinical studies, might have a superior immunogenic profile than photons. Proton-IT combination is being studied currently by various groups in lung , head neck and brain tumors, and should be evaluated further in other subsites to replicate preclinical outcomes in a clinical setting. In this review, we summarize the currently available evidence for combinatorial approaches and feasibility of proton and IT combination, and thereafter highlight the emerging challenges for practical application of the same in clinics, while also proposing plausible solutions.