Abstract P18: Functional Consequences of Structural Variants Arising from Extracellular Domain Mutations in EGFR

Abstract Background: Epidermal growth factor receptor (EGFR) is an oncogene frequently mutated in cancers. Around half of Asian non-small cell lung cancer (NSCLC) tumours harbour activating EGFR mutations, the most prevalent variants being exon19 deletion and L858R point mutation, with enhanced response to tyrosine kinase inhibitors (TKIs). EGFR extracellular domain (ECD) mutations have been detected in NSCLC tumours, particularly among resistant tumours, with limited understanding. Here, we hypothesise that ECD mutations may play a role in driving oncogenesis. Methods: A recurring mutation found in advanced NSCLC patients was selected as a proof-of-concept. In vitro cell culture model was established using genomic editing. Functional assays and immunofluorescence staining were performed to understand how the mutation affects cancer hallmarks and localisation of EGFR respectively. Results: Functional profiling suggested that mutation does not affect certain canonical hallmarks of cancer and EGFR downstream signalling pathways. However, the stability of the mutant protein is reduced, affecting overall basal EGFR protein expression level in the mutant cell lines. In addition, mutation affects canonical binding to the epidermal growth factor ligand. Interestingly, there is a localisation of mutant EGFR protein to the endoplasmic reticulum (ER), away from the cell surface membrane. Conclusion: ECD mutations may contribute to an under-represented mode of mechanism driving oncogenesis. Our data suggest that recurring variants among tumours may drive tumour progression through a non-canonical pathway affecting mutant protein accumulation, possibly leading to ER stress. It is hoped that by gaining further insights into ECD mutation driven cancer, we will be able to delineate their role in oncogenesis and guide precision medicine by exploring alternative therapeutics targeting ECD mutations to achieve cancer remission. Citation Format: Hui Qing Yeo, Jun Ting Teo, Aishwary Shivgan, Kannan Srinivasaraghavan, Azhar Bin Ali, Chandra Verma, Li Ren Kong, Boon Cher Goh. Functional Consequences of Structural Variants Arising from Extracellular Domain Mutations in EGFR [abstract]. In: Proceedings of Frontiers in Cancer Science 2025; 2025 Nov 5-7; Singapore. Philadelphia (PA): AACR; Cancer Res 2026;86(13_Suppl):Abstract nr P18.