Combinatorial strategies of radiotherapy and immunotherapy in nasopharyngeal carcinoma

Immunotherapy and radiation therapy (RT) have each demonstrated clinical success in the treatment of nasopharyngeal carcinoma (NPC) when utilized independently. Several characteristics of NPC make it particularly well suited for immunotherapeutic strategies, such as the association with viral infections like EBV and human papilloma virus (HPV), upregulation of PD-L1 expression, and the high number of tumor infiltrating lymphocytes. Immune checkpoint blockade is one such immunotherapeutic strategy that is gaining popularity rapidly. However, clinical benefit of immunotherapy using immune checkpoint inhibitors has been limited to only a small subset of patients with existing T cell responses. Additionally, they are frequently associated with dose-limiting immune-related toxicities. On the other hand, RT is a conventional strategy for NPC treatment, which has demonstrated high efficacy in local tumor control and has also been reported to exhibit immune modulatory effects. However, the abscopal effect of RT alone, i.e., the regression of distant metastases outside of the irradiation field, remains a rare phenomenon. Furthermore, RT treatment efficacy is also limited by radioresistance and radiation-related toxicities. Hence, the combination of RT and immunotherapy has the potential to improve treatment efficacy over either individual therapies alone. Here, we reviewed the clinical problem in locally advanced and recurrent/metastatic NPC, and discussed how combinatorial RT and immunotherapeutic strategies can be relevant to NPC treatment in each clinical scenario by examining the underlying mechanisms involved in the different strategies.