Background
Several good results of clinical trial of nivolumab or involving nivolumab in advanced esophageal squamous cell carcinoma were reported. However, the response rate was still poor. A rare phenomenon called the “abscopal effect” refers to the regression of not only the irradiated tumor but also non-irradiated distant tumors after local radiotherapy. The mechanism is not completely clear, but it is thought that the activation of anti-tumor immunity induced by radiotherapy is the main factor.