Impact of HER2 Aberrations on EGFR-TKI Treatment Outcomes in Lung Tumors Harboring EGFR Mutations: A HER2-CS STUDY Subset Analysis.

9056 Background: Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) are a key treatment for EGFR-mutated non-small-cell lung carcinoma (NSCLC). To date, a biomarker to predict whether NSCLC will exhibit a short- or long-term response to first- or second-generation EGFR-TKIs has not been established for clinical use. Human epidermal growth factor receptor-2 (HER2) aberrations are mechanisms for acquired resistance to EGFR-TKIs; however, their impact on EGFR-TKI therapy outcomes in EGFR-mutant NSCLC has not yet been systematically evaluated. Methods: Patients with advanced NSCLC were prospectively registered from more than 35 institutes (HER2-CS STUDY UMIN 000017003). EGFR mutations or anaplastic lymphoma kinase gene translocations were assessed at each institution using a commercially approved test. HER2 protein expression levels were determined by immunohistochemistry (IHC) using the Ventana I-VIEW PATHWAY anti-HER-2/neu (4B5). The IHC status scoring system applied to gastric cancer was used. Results: Of 1,126 screened patients with NSCLC, 354 (31.8%) had EGFR-mutated tumors, and the HER2 protein statuses were as follows: IHC0 (n = 71, 26%), IHC1+ (n = 148, 53%), IHC2+ (n = 51, 18%), and IHC3+ (n = 7, 3%). The patients’ demographics were almost identical in those with lung tumors harboring EGFR mutations and HER2-IHC2+/3+ (group P) or EGFR mutations and HER2-IHC0/1 (group N). The EGFR-TKI response rates were not different between these groups (Table). However, group P showed significantly shorter time to EGFR-TKI treatment failure than group N (median 19.1 vs. 13.3 months; log rank p = 0.038). Conclusions: These data from a large prospective cohort show that HER2 protein expression in EGFR-mutant NSCLC may have a negative impact on the effect of EGFR-TKIs. A clinical trial of EGFR/HER2-TKIs (e.g., afatinib) is warranted for this population. [Table: see text]