Purpose: KRAS is among the most commonly mutated oncogene in cancer including non–small cell lung cancer (NSCLC). In early clinical trials, inhibitors targeting G12C-mutant KRAS have achieved responses in some patients with NSCLC. Possible intrinsic and acquired resistance mechanisms to KRAS G12C inhibitors are not fully elucidated and will likely become important to identify. Experimental Design: To identify potential resistance mechanisms, we defined the sensitivity of a panel of KRAS G12C–mutant lung cancer cell lines to a KRAS G12C inhibitor, AMG510. Gene set enrichment analyses were performed to identify pathways related to the sensitivity, which was further confirmed biochemically. In addition, we created two cell lines that acquired resistance to AMG510 and the underlying resistance mechanisms were analyzed. Results: KRAS expression and activation were associated with sensitivity to KRAS G12C inhibitor. Induction of epithelial-to-mesenchymal transition (EMT) led to both intrinsic and acquired resistance to KRAS G12C inhibition. In these EMT-induced cells, PI3K remained activated in the presence of KRAS G12C inhibitor and was dominantly regulated by the IGFR–IRS1 pathway. We found SHP2 plays a minimal role in the activation of the PI3K pathway in contrast to its critical role in the activation of the MAPK pathway. The combination of KRAS G12C inhibitor, PI3K inhibitor, and SHP2 inhibitor resulted in tumor regressions in mouse models of acquired resistance to AMG510. Conclusions: Our findings suggest that EMT is a cause of both intrinsic and acquired resistance by activating the PI3K pathway in the presence of KRAS G12C inhibitor.

Considering the increasing number of identified driver oncogene alterations, additional genetic tests are required to determine the treatment for advanced non‐small‐cell lung cancer (NSCLC). Next‐generation sequencing can detect multiple driver oncogenes simultaneously, enabling the analysis of limited amounts of biopsied tissue samples. In this retrospective, multicenter study (UMIN ID000039523), we evaluated real‐world clinical data using the Oncomine Dx Target Test Multi‐CDx System (Oncomine DxTT) as a companion diagnostic system. Patients with NSCLC who were tested for a panel of 46 genes using the Oncomine DxTT between June 2019 and January 2020 were eligible for enrollment. Patients from 19 institutions affiliated to the West Japan Oncology Group were recruited. The primary endpoint of the study was the success rate of genetic alteration testing in four driver genes (EGFR, ALK, ROS1, and BRAF) using the Oncomine DxTT. In total, 533 patients were enrolled in the study. The success rate of genetic alteration testing for all four genes was 80.1% (95% CI 76.5%‐83.4%). Surgical resection was associated with the highest success rate (88.0%), which was significantly higher than that for bronchoscopic biopsy (76.8%, P = .005). Multivariate analysis revealed a significant difference for surgical resection alone (P = .006, 95% CI 1.36‐6.18, odds ratio 2.90). Although the success rate of genetic alteration testing immediately after Oncomine DxTT induction was not sufficient in this study, optimizing specimen quantity and quality may improve the use of driver gene testing in clinical settings.