Successful osimertinib retreatment after extremely early onset severe pneumonitis in first-line treatment of lung adenocarcinoma.

Drug-induced pneumonitis is rare, and can result in death. Here, we present a report of a patient with adenocarcinoma harboring EGFR exon 19 deletion mutation treated with osimertinib as first-line treatment. After six days of treatment, extremely early onset severe pneumonitis was diagnosed. Discontinuation of osimertinib as well as administration of corticosteroid, and retreatment with osimertinib were successful. This case report highlights that extremely early onset severe pneumonitis can occur after osimertinib administration, and retreatment of osimertinib may be a useful treatment option after resolution of pneumonitis.