Real World Characteristics and Clinical Outcomes of HER2-Mutant Non–Small Cell Lung Cancer Patients Detected by Next-Generation Sequencing

PURPOSE: This study was conducted to investigate the clinical characteristics of patients with advanced non–small cell lung cancer (NSCLC) harboring human epidermal growth factor receptor 2 (HER2) mutations and to evaluate response to standard treatment and HER2-targeted agents. MATERIALS AND METHODS: Using tissue and/or blood next-generation sequencing, we identified 44 patients with NSCLC harboring HER2 mutations who were treated at Severance Hospital between December 2016 and February 2021. Clinical data, including patient characteristics, mutation status, incidence of metastasis for distant lesions, and response to chemotherapy, were retrospectively analyzed. RESULTS: The median age was 58 years, and 61% of the patients were female. Most patients (64%) were never-smokers. Adenocarcinoma was the most predominant subtype (98%). A total of 66% of the patients had extrathoracic metastatic lesions, and 32% had intracranial lesions at initial presentation. The median time to the development of brain metastasis was 15.6 months (range, 2.4 to 43.7). The most common type of HER2 mutation was 12 base pair in-frame insertion in exon 20, A775_G776insYVMA. Of the 44 patients, two had concomitant driver mutations, one with epidermal growth factor receptor (EGFR) mutation (V769M), and one with BRAF mutation (V600E). Patients treated with pemetrexed-based chemotherapy (75%) had an overall response rate (ORR) and progression-free survival (PFS) of 30% and 8.3 months (95% confidence interval [CI], 3.9 to 12.7), respectively. The ORR and PFS of HER2-targeted agent treated patients (14%) were 0.0% and 1.9 months (95% CI, 0.1 to 2.8), respectively. CONCLUSION: Given its distinct characteristics and treatment responses, novel treatment strategies for HER2-mutant NSCLC should be developed promptly to improve survival outcomes of patients.