We present the case of a 48-year-old woman who was referred to us with breathing difficulties. A large-volume left pleural effusion was noted, and she was diagnosed with pleural dissemination of lung adenocarcinoma by thoracoscopic examination under local anesthesia. The expression rate of programmed cell death-ligand 1 (PD-L1) was 90%, and chemotherapy was initiated with pembrolizumab. The pleural dissemination reduced promptly, and tumor marker levels decreased after four courses of chemotherapy.
When the positon emission tomography/computed tomography examination was performed, the fluorodeoxyglucose (FDG) accumulation in the disseminated lesion had disappeared, but bilateral hilar hyperparathyroid lymph node enlargement was noted, which displayed significant fluorodeoxyglucose uptake. A thoracoscopic lymph node biopsy was performed, from which we recognized epithelioid granuloma without necrosis, and diagnosed the patient with a sarcoid-like reaction. There have been few reports of sarcoid-like reactions after pembrolizumab administration for lung adenocarcinoma, and as such, this should be considered as a valuable case.