HER2 Amplification: A Potential Mechanism of Acquired Resistance to EGFR Inhibition in EGFR-Mutant Lung Cancers That Lack the Second-Site EGFRT790M Mutation

Abstract

EGFR-mutant lung cancers eventually become resistant to treatment with EGFR tyrosine kinase inhibitors (TKIs). The combination of EGFR-TKI afatinib and anti-EGFR antibody cetuximab can overcome acquired resistance in mouse models and human patients. Since afatinib is also a potent HER2 inhibitor, we investigated the role of HER2 in EGFR-mutant tumor cells. We show in vitro and in vivo that afatinib plus cetuximab significantly inhibits HER2 phosphorylation. HER2 overexpression or knockdown confers resistance or sensitivity, respectively, in all studied cell line models. Fluorescent in situ hybridization analysis revealed that HER2 was amplified in 12% of tumors with acquired resistance versus only 1% of untreated lung adenocarcinomas. Notably, HER2 amplification and EGFR T790M were mutually exclusive. Collectively, these results reveal a previously unrecognized mechanism of resistance to EGFR TKIs and provide a rationale to assess the status and possibly target HER2 in EGFR mutant tumors with acquired resistance to EGFR TKIs.

Analytical Validation of BRAF Mutation Testing from Circulating Free DNA Using the Amplification Refractory Mutation Testing System

“…89 ERBB2 amplification has also been reported rarely as a secondary event in patients with sensitizing EGFR mutations and as a potential mechanism of resistance following treatment with EGFR inhibitors. 90 In this context and with current evidence, routine standalone testing for ERBB2 mutations is not indicated outside a clinical trial. Nevertheless, when broader testing is performed through a multiplex assay or NGS, it is appropriate to include ERBB2 as part of the testing, as it may identify patients to be directed to clinical trialsdin this context, testing for sequence alterations in ERBB2, particularly insertions/duplications in exon 20, which have been associated with response to treatment with targeted inhibitors of ERBB2 in case reports and small series.…”

“…The detection of the EGFR T790M mutation in this setting has become clinically necessary because of the development of third-generation EGFR TKIs, such as osimertinib, which are active in the presence of this mutation. 223,224 However, although rare responses have been reported to third-generation inhibitors in EGFR T790Menegative disease, 225 such cases may harbor other resistance mechanisms such as MET or ERBB2 amplification 90,114,226 that may be more effectively targeted by other agents. Therefore, determining appropriate therapy in the setting of secondary clinical resistance to an EGFR inhibitor requires knowledge of the presence or absence of the T790M mutation.…”

Genetic modifiers of EGFR dependence in non-small cell lung cancer

“…Mounting evidence supports the existence of several genetic modifiers of EGFR dependence in EGFR-mutant NSCLC, which can reduce the degree to which these tumors rely on EGFR and thereby contribute to EGFR TKI resistance (8). Examples include amplification of the MET receptor tyrosine kinase (RTK) (9), activation of the NF-κB pathway (8), amplification of the HER2 (ERBB2) RTK (10), amplification of the CRKL gene (11), and activation of the AXL kinase (12). Notably, MET bypass can be reciprocally achieved via EGFR activation in MET-dependent cells (13), and analogous examples of reciprocal kinase switching have been reported in other kinase-driven cancer models (14,15).…”

Successful treatment of a patient with Li–Fraumeni syndrome and metastatic lung adenocarcinoma harboring synchronous EGFR L858R and ERBB2 extracellular domain S310F mutations with the pan-HER inhibitor afatinib

“…22 Accumulating evidence has demonstrated cross-talk between HER family members in the development of acquired resistance to EGFR-TKI therapy. 26,27 HER2 overexpression also can confer resistance to EGFR-TKIs in cell line models and the HER2 gene was found to be amplified in a significant fraction of both murine and human tumors with acquired resistance to erlotinib. As noted earlier, re-biopsy of such a unique tumor upon progression could provide further clues as to the contribution of the two synchronous oncogenic pathways to acquired resistance.…”