Abscopal Effect Following Immunotherapy and Combined Stereotactic Body Radiation Therapy in Recurrent Metastatic Head and Neck Squamous Cell Carcinoma: A Report of Two Cases and Literature Review.

OBJECTIVE: We present two patients with recurrent, metastatic head and neck squamous cell carcinoma (R/M HNSCC) after platinum-based chemotherapy and radiotherapy (RT) with complete response via abscopal effect following combined immunotherapy (IT) and stereotactic body radiation therapy (SBRT). We review the literature for patients undergoing combined treatment with IT and RT to identify potential cases of abscopal response. STUDY DESIGN: This is a case series with a contemporary review of the literature. METHODS: Retrospective chart review identified two patients with potential abscopal responses after IT and RT for R/M HNSCC. The MEDLINE database was queried using the search terms "abscopal AND head and neck squamous cell carcinoma" and "immunotherapy AND stereotactic body radiation therapy." RESULTS: Two patients with metastatic HNSCC developed complete responses via a possible abscopal effect following combined SBRT and IT. Interim follow-up of both patients revealed a sustained, complete response. We examine the immunogenic effects of RT and report the first cases of potential abscopal effect for R/M HNSCC. We also review several preclinical studies demonstrating the synergistic efficacy of combined RT and IT with a discussion of possible mechanism. CONCLUSION: Observation of abscopal effect with combined IT and RT is currently under investigation through several preclinical studies and trials. To the best of our knowledge, these are the first two reported cases of abscopal effect for patients with HNSCC. We report two patients with R/M HNSCC with sustained, complete response after systemic IT and local RT.