The Abscopal Effect in Head-and-Neck Squamous Cell Carcinoma Treated with Radiotherapy and Nivolumab: A Case Report and Literature Review

Introduction: The abscopal effect is a rarely observed outcome of radiotherapy wherein there is a reduction in metastatic disease burden outside of the targeted treatment area. Likely due to an in situ vaccine effect of radiotherapy, the abscopal effect may be augmented by immunotherapy. This report is the first case of the abscopal effect observed in metastatic head-and-neck squamous cell carcinoma (HNSCC) treated with concurrent radiotherapy and single-agent nivolumab. Case Description: An otherwise healthy 57-year-old man underwent craniofacial resection and adjuvant chemoradiotherapy for advanced sinonasal squamous cell carcinoma. Distant metastatic disease developed shortly after primary treatment, and immunotherapy in the form of nivolumab was initiated. Subsequent oligometastatic progression despite immunotherapy prompted palliative radiotherapy to a single metastasis due to pending symptomatology. Post-radiotherapy, the abscopal effect was observed with all distant sites of metastatic disease shrinking. Five months following treatment, a sustained reduction in disease burden has been demonstrated. Summary: We present the first case of the abscopal effect in a patient with metastatic hnscc treated with palliative radiotherapy concurrent with single-agent nivolumab immunotherapy, and only the third case of the abscopal effect in metastatic head-and-neck cancer. Dual treatment with immunotherapy and radiotherapy may be an important treatment option in the future, mediated through the abscopal effect.