Abstract LB285: HER2 signaling drives drug tolerant persisters to first line amivantamab and lazertinib in EGFR Mutant non small cell lung cancer

Abstract Lung cancer remains the leading cause of cancer-related deaths worldwide. Non-small cell lung cancer (NSCLC), the most common subtype, frequently harbors activating mutations in the epidermal growth factor receptor (EGFR) gene. In 2024, the first-line combination therapy of amivantamab and lazertinib was approved by the FDA based on findings from the MARIPOSA trial, which demonstrated superior progression-free survival compared to osimertinib monotherapy. However, mechanisms of drug-tolerant persisters remain poorly understood. This study investigates the mechanisms underlying resistance to amivantamab-lazertinib combination therapy using multi-omics analyses. Methods: Fresh tumor samples were obtained from a treatment-naïve EGFR exon 19 deletion (ex19del) patient and transplanted into the flanks of athymic nude mice to establish patient-derived xenograft (PDX) models. The mice were treated in vivo with amivantamab-lazertinib for 10 days, followed by analyses including single-cell and bulk RNA sequencing (RNA-seq), whole-exome sequencing (WES), and immunohistochemistry (IHC) to assess early-phase treatment response.A subset of mice was treated with amivantamab-lazertinib for 10 days, after which treatment was stopped, allowing tumors to regrow to a volume of 500 mm3 over 30 days to evaluate potential genetic and transcriptomic remodeling induced by the therapy. Results: WES revealed HER2 amplification in 60% of tumors analyzed at 30 days post-treatment (n=6), compared to untreated controls. Bulk RNA-seq confirmed significant ERBB2 mRNA increase in tumors from both the 10-day and 30-day groups. Single-cell RNA-sequencing (scRNA-seq) identified drug-tolerant persister clusters (DTPs) with significantly higher enrichment of ERBB2-related signaling pathways and epigenetic regulators, including the histone modification pathway.In the 30-day tumors, scRNA-seq further revealed that cancer-associated fibroblasts (CAFs) interacted with tumor clusters via ERBB2 signaling. In vitro studies using cell lines supported these findings, showing that osimertinib and lazertinib monotherapy did not increase HER2 expression, while the combination of amivantamab and lazertinib significantly induced HER2 expression. Additionally, HER2 IHC of 10-day and 30-day tumors both showed significant overexpression of HER2 protein.Finally, a patient who progressed after first-line amivantamab-lazertinib therapy was found to harbor HER2 amplification (copy number >10), confirmed through silver-enhanced in situ hybridization (SISH) of the tumor at the time of progression. This patient was subsequently treated with a HER2 tyrosine kinase inhibitor (TKI) and demonstrated a favorable tumor response. Conclusion: Our results reveal that elevated HER2 expression contribute to resistance to amivantamab-lazertinib therapy. During the early-phase response, epigenetic mechanisms, such as histone modifications, may regulate ERBB2 expression. These findings were further validated by identifying HER2 amplification in a patient who progressed after amivantamab-lazertinib therapy and responded to HER2-directed TKI treatment. Our results suggest that targeting the HER2 axis may represent a viable therapeutic strategy for patients who progress following amivantamab-lazertinib combination therapy. Citation Format: Joosung Gabriel Shim, Youwon Lee, Jii Bumm Lee, Min Hee Hong, Byoung Chul Cho, Sun Min Lim. HER2 signaling drives drug tolerant persisters to first line amivantamab and lazertinib in EGFR Mutant non small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr LB285.