Abstract
BACKGROUND: It remains unclear why radiation clinically provides a synergistic effect when combined with immune checkpoint inhibitors such as nivolumab. The purpose of our study was to retrospectively evaluate whether the therapeutic efficacy of nivolumab is improved as a result of a history of radiotherapy (RT) in patients with previously treated advanced non-small cell lung cancer (NSCLC). METHODS: From February 2016 to December 2017, 124 consecutive patients were administered nivolumab for pretreated advanced NSCLC. The patients were divided into RT and non-RT groups. RESULTS: Sixty-six (53%) of the 124 patients had been administered RT before the initiation of nivolumab, 52 (42%) received extracranial RT, and 40 (32%) were treated with thoracic RT. The median number of nivolumab cycles was 4 (range: 1-43). The overall response rate (ORR) and disease control rate (DCR) of nivolumab in all patients were 28.0% and 58.4%, respectively. The ORR (36.4%) was significantly higher in patients who had received previous RT than in patients who had not received any RT (19%). The therapeutic efficacy of nivolumab was particularly noteworthy in patients with non-adenocarcinoma and squamous cell carcinoma histology administered extracranial RT, with ORRs of 48.3% and 52.6%, and DCRs of 87.1% and 84.2%, respectively. CONCLUSION: Previous RT was an independent prognostic marker of favorable prognosis after nivolumab administration and improved the response rate to nivolumab treatment. Previous RT was clinically identified to have a synergistic effect with nivolumab treatment, increasing the response rate and improving the outcome of patients with advanced NSCLC.