Successful Chemotherapy for Diffuse Cystic Lung Metastases during Targeted Therapy with Osimertinib in a Patient with Non-Small-Cell Lung Cancer: A Literature Review and a Rare Case Report

IntroductionDiffuse lung cysts occur owing to several diseases; however, diffuse cystic lung metastases are very rare in the case of lung cancer. We report a rare case of diffuse cystic lung metastases from lung adenocarcinoma and reviewed previously reported cases of cystic lung metastases for lung cancer and determined their characteristics.Case PresentationA 78-year-old Japanese woman with advanced lung adenocarcinoma was positive for the epidermal growth factor receptor gene mutation exon 21 L858R and had been treated with osimertinib. She presented with multiple bilaterally positioned thin-walled lung cysts and pneumothorax. Lung cysts were diagnosed as cystic lung metastases from lung cancer, and carboplatin, pemetrexed, and pembrolizumab were subsequently administered. All cysts markedly decreased in size, and some disappeared.ConclusionEffective treatment methods for cystic lung metastases from lung cancer have not been reported. To our knowledge, this is the first case of cystic lung metastases that were successfully treated with chemotherapy.