Human epidermal growth factor receptor 2 (HER2) mutation and amplification are distinct molecular targets in lung cancer, but the specific targeted therapy for their coexistence is undetermined. Personalized targeted therapy is based on mutation type, with different mutations requiring different treatment. A 64-year-old Chinese woman was diagnosed with advanced lung adenocarcinoma. She was determined as having insertion mutations in exon 20 of the HER2 gene (c.2326G > TTGT) by the amplification refractory mutation system (ARMS) and HER2 gene amplification (HER2/CEP17 ratio 2.6) by fluorescence in situ hybridization (FISH). Thereafter, she was treated with afatinib as first-line therapy, to which she responded. After 2 months, the tumor lesion decreased in size. Computed tomography (CT) follow-up showed stable lung lesions, although she later developed multiple brain metastases and subsequently died of brain failure. Lung adenocarcinoma with coexistent HER2 mutation and amplification is relatively uncommon and has no reported cases on targeted therapy. This case was important because it showed effective response to afatinib and provides evidence to help clinicians identify the therapeutic regimen for such patients.
Keywords: HER2 amplification; Human epidermal growth factor receptor 2 (HER2); afatinib; case report; lung adenocarcinoma; mutation.