Trastuzumab deruxtecan (DS8201) for advanced non-small cell lung cancer with HER2 exon 20 insertion mutation: a case report.

An antibody-drug conjugate (ADC) of human epidermal growth factor receptor-2 (HER2) provides effective treatment for patients with HER2-positive non-small cell lung cancer (NSCLC). Exon 20 insertion mutations are the most common among HER2 mutations. This mutant subtype is highly drug-resistant, and patients receiving conventional treatment often have a poor prognosis. Trastuzumab deruxtecan (T-DXd), a novel anti-HER2 ADC, has emerged as a novel treatment option for HER2-positive (mutated, expressed, amplified, alternated) NSCLC, based on several studies and reported results. Herein, we report a case of stage IV NSCLC with HER2 exon 20 mutation in a 52-year-old male patient whose tumor recurred after radical resection of pulmonary carcinoma, who could not tolerate chemotherapy, and presented with bone metastasis. After treatment with T-DXd, the tumor significantly regressed and bone metastasis improved, maintaining a state of no progression for 21 months. This case report evidences the use of T-DXd in the treatment of NSCLC with HER2 exon 20 insertion mutation.