Response to furmonertinib in a patient with non-small cell lung cancer harboring HER2 exon 21 insertion mutation: a case report.

Background: This is the first case report describing a patient with non-small cell lung cancer (NSCLC) harboring two rare human epidermal growth factor receptor 2 (HER2) exon 21 insertion mutations, who responded to furmonertinib treatment. Furmonertinib maybe one effective and economical treatment for NSCLC patients harboring HER2 mutations with minor side effects. Case description: We present a case report of a 49-year-old female diagnosed with stage IV lung adenocarcinoma who complained of irritating dry cough symptoms followed by chest tightness. Firstly, we describe the patient's treatment history, including failed third-line combination treatments of systemic chemotherapy with bevacizumab or carrelizumab or anlotinib, primary lung tumor recurrence, bilateral lung metastases progression, and new brain metastatic lesion detection. Next, we detail the patient's fourth-line treatment with radiotherapy for brain metastases and two cycles of bevacizumab plus Abraxane and cisplatin, however, the disease progressed and relapsed. After that, comprehensive genomic profiling revealed two HER2 exon 21 insertion mutations. Subsequently, the patient received targeted therapy with furmonertinib and achieved 11 months of progression-free survival. The patient received pyrrotinib therapy for 2 months after disease progression, but the disease continued to progress. In October 2023, the patient received therapy with furmonertinib again, and a month later, the disease went into partial remission. However, the patient died due to hypoproteinemia combined with severe pneumonia in December 2023. Conclusion: Furmonertinib may be effective for NSCLC patients with HER2 T8962A and L869R mutations and further studies are needed to confirm these results in prospective clinical trials.