Abstract
A 60-year-old woman was diagnosed with cT4N3M1c stage IVB lung adenocarcinoma with epidermal growth factor receptor mutation of exon19 deletion. After one month of treatment with osimertinib, a cough and diffuse ground glass opacities were observed in the bilateral lung field. Based on the clinical course and the exclusion of other etiologies, osimertinib-induced pneumonitis was diagnosed. The shadows resolved after osimertinib was discontinued. However, brain metastasis and leptomeningeal metastasis developed 20 months later; therefore, osimertinib was re-administered without concomitant corticosteroids. The pulmonary lesion and leptomeningeal metastasis were successfully treated without recurrence of drug-induced pneumonitis for eight months.