Successful Rechallenge with Osimertinib after Very Acute Onset of Drug-Induced Pneumonitis.

Drug-induced interstitial lung disease (DI-ILD) is a rare, yet life-threatening complication associated with tyrosine-kinase inhibitor (TKI) therapy. Third-generation epidermal growth factor receptor-TKI, osimertinib use can be associated with a benign radiological finding called transient asymptomatic pulmonary opacities that can be confused with an infectious pulmonary process resulting in overtreatment with antibiotics or premature treatment withdrawal or severe DI-ILD. In this case, our patient with newly diagnosed metastatic non-small cell lung cancer on treatment with osimertinib developed very early onset severe DI-ILD (grade-IV) with a unique pattern of pulmonary involvement and was treated with high-dose corticosteroids with a response. She was later successfully rechallenged with osimertinib and responded well to the treatment. Our case highlights the importance of being cognizant of the possibility that DI-ILD can rarely occur within a week of treatment initiation with osimertinib and safe reintroduction of the drug is possible in select patients following complete resolution of pulmonary radiographic findings and clinical symptoms even with high-grade adverse events.