Primary lung cancer treatable with radical resection after complete remission with pembrolizumab therapy following gemcitabine and carboplatin chemotherapy for multiple metastases of bladder cancer

INTRODUCTION: We report a patient with the complete remission of multiple metastases and primary bladder lesions of bladder cancer who developed primary lung cancer requiring radical resection. CASE PRESENTATION: A 68‐year‐old man diagnosed with invasive bladder cancer, right hydroureteronephrosis, and multiple metastases were administered six courses of gemcitabine and carboplatin chemotherapy and thereafter has been receiving pembrolizumab therapy. Bladder cancer and multiple metastases decreased in size, whereas a ground‐glass opacity lesion in the lung gradually increased in size. Fluorodeoxyglucose‐positron emission tomography revealed the accumulation of fluorodeoxyglucose in the ground‐glass opacity lesion only. The patient was diagnosed with primary lung cancer and underwent a thoracoscopic lobectomy. Histopathological findings showed ALK‐negative, EGFR L858R mutation‐positive invasive adenocarcinoma with a programmed death‐ligand 1 tumor proportion score of less than 1%. CONCLUSION: This is the first case report of patients with the complete remission of multiple metastases of bladder cancer who developed primary lung cancer requiring radical resection.