Organizing pneumonia after thoracic radiotherapy followed by anti-PD-1 antibody treatment for patients with lung cancer: Three case reports.

Anti-PD-1 antibodies and thoracic radiation therapy (TRT) generate adverse events, including pneumonitis. However, there is limited information about potential overlapping toxicity of anti-PD-1 antibodies administered after TRT. Herein, we report three cases. The first case was of a man in his 80s with squamous cell lung cancer (cT2aN0M0 stage IB). Twelve months after TRT, tumor regrowth was observed, and the patient was administered nivolumab. Twenty-four months after TRT, computed tomography (CT) showed organizing pneumonia (OP). The second case was of a man in his 70s with squamous cell lung cancer. He underwent surgery for pT3N1M0 stage IIIA; however, mediastinum lymph node metastasis developed. Therefore, he received TRT for the mediastinum lymph node metastasis. One month after the completion of TRT, nivolumab was administered. Two months after TRT, an OP diagnosis was made. The third case was of a man in his 60s with an unknown type of lung cancer. He received TRT for cT4N2M0 stage IIIB. Fourteen months after TRT, tumor regrowth was observed, thus, nivolumab was administered. Twenty-seven months after TRT, an OP diagnosis was made. These case reports draw attention to OP after TRT and anti-PD-1 antibody administration despite low V20. Careful follow-up of such patients is advised considering synergistic adverse events.