Successful Rechallenge of Trastuzumab Deruxtecan Following Early Detection of ILD in a Patient with Non-small Cell Lung Carcinoma Harboring HER2 Exon 20 Insertion

We herein report the case of a 78-year-old woman with non-small cell lung carcinoma (NSCLC) harboring a HER2 exon 20 insertion, who developed grade 1 trastuzumab deruxtecan (T-DXd)-induced interstitial lung disease (ILD) during third-line therapy. Oral corticosteroid administration led to radiological improvement, enabling T-DXd re-administration at a reduced dose. She received eight additional cycles (nine in total), resulting in tumor regression without ILD recurrence. Given that T-DXd is currently the only approved HER2-targeted therapy for NSCLC in our country, this case underscores the importance of early detection and appropriate management of ILD to maximize the therapeutic benefits.