Dramatic, significant metabolic response to a one‐time pembrolizumab treatment following a relapse of pre‐existing organizing pneumonia in a patient with advanced non‐small cell lung cancer: A case report

Immune checkpoint inhibitors can often trigger immune‐related adverse events (irAEs), such as relapse of pre‐existing interstitial pneumonia. Here, we report the case of an 88‐year‐Japanese man diagnosed with advanced lung adenocarcinoma with a high tumor proportion score of programmed death‐ligand 1. Six years earlier, he had developed organizing pneumonia (OP), a subtype of interstitial pneumonia, that was treated with steroid pulse therapy maintained with prolonged prednisolone administration. We initiated pembrolizumab as the first‐line treatment. One month after the first pembrolizumab administration, high resolution computed tomography (HRCT) of the chest demonstrated ground‐glass opacities and consolidations. We suspected pembrolizumab‐induced OP relapse, an irAE. His oxygenation was normal; therefore, we discontinued pembrolizumab without additional treatment for OP relapse. Four months after OP relapse, HRCT showed no new findings. After significant amelioration of OP, although the size of the tumor shadow remained the same on HRCT, positron emission tomography‐computed tomography demonstrated the disappearance of the standardized uptake value of the primary tumor, mediastinal lymph nodes, and pleural nodules. In conclusion, this is the first report of a dramatic, significant metabolic response after a single pembrolizumab treatment despite the relapse of pre‐existing OP in a patient with advanced lung adenocarcinoma.