Anti‐PD‐1 monoclonal antibody‐resistant esophageal squamous cell carcinoma showing the abscopal effect: A case report with T‐cell receptor/B‐cell receptor repertoire analysis

Several clinical trials of nivolumab have reported good results, including those in patients with advanced esophageal squamous cell carcinoma. However, the response rate of this drug remains poor. Notably, a rare phenomenon called abscopal effect refers to the regression of irradiated and nonirradiated distant tumors after local radiotherapy. Although the mechanism of this effect remains unclear, the antitumor immunity induced by radiotherapy is considered to be the most important factor.A 66-year-old man with recurrent nivolumab-resistant esophageal squamous cell carcinoma along with left-side cervical and abdominal para-aortic lymph node metastases was treated with a 40 Gy (10 fractions) dose of radiotherapy to the left-side cervical lymph node metastasis as a palliative treatment, which caused neck pain. In addition, nivolumab administration was resumed the day after completion of radiotherapy. Three months after radiotherapy, the irradiated lesion on the left neck had regressed to a scar-like lesion. Furthermore, the previously progressive abdominal para-aortic lymph nodes outside the irradiation area shrank (abscopal effect). T-cell receptor and B-cell receptor (TCR/BCR) repertoire analyses before and after radiotherapy revealed that radiotherapy led to changes in the TCR/BCR repertoire.Changes in the TCR/BCR repertoire may be a part of the mechanism underlying the abscopal effect. The findings of the present case suggest that the combination of immune checkpoint inhibitors and radiotherapy is a promising treatment approach even for patients with immune checkpoint inhibitor-resistant cancer.