Delayed pseudoprogression of lung adenocarcinoma accompanied with interstitial lung disease during chemotherapy after nivolumab treatment

A 62‐year‐old Japanese female with primary lung adenocarcinoma received seven cycles of nivolumab as an eighth line of chemotherapy until she presented with hemoptysis. After transcatheter arterial embolization therapy, she received subsequent chemotherapy with paclitaxel and S−1. Four weeks later, a chest computed tomography examination revealed infiltrative shadows mainly in the right lung field, in addition to enlargement of the lung metastasis in the right middle lung lobe. Bronchofiberscopic examination revealed infiltration of lymphocytes without any malignant cells in the right segment 1 of the lung, which suggested interstitial lung disease. Corticosteroid therapy not only improved the infiltrative shadows but also reduced the lung metastasis. Even after the infiltrative shadows improved, the lung metastasis reduced further. This phenomenon resembles manifestation of pseudoprogression during treatments with immune checkpoint inhibitors, such as nivolumab.