Detection of Overlooked Rare EGFR Mutations in Non‐small Cell Lung Cancer Using Multigene Testing

ABSTRACT Background Recognizing rare molecular variants of driver mutations poses a challenge in precision oncology, particularly for treatment of non‐small cell lung cancer (NSCLC). In this study, we aimed to determine whether Oncomine Dx Target Test Multi‐CDx System (ODxTT), the most widely used genetic test for NSCLC in Japan, potentially overlooks druggable EGFR mutations. Materials and Methods Among 418 patients who underwent molecular testing using ODxTT at our hospital, 267 were diagnosed with adenocarcinoma. No mutations were reported in 82 of these cases. For these 82 cases, we searched for EGFR mutations in exons 18–21 by examining the binary alignment map file. Once a mutation was identified, its pathological significance was evaluated using the ClinVar database to determine whether ODxTT had overlooked any actionable EGFR mutations. Results Mutations in EGFR exons 19 and 18 were identified in six and four cases, respectively. Three, six, and none of these variants were detectable using the Cobas EGFR Mutation Test v2, Lung Cancer Compact Panel, and Amoy Dx, respectively. Of the 10 patients, five were subsequently treated with EGFR TKI; three showed partial response, one had stable disease, and one had progressive disease. Conclusions ODxTT failed to identify 10 actionable EGFR mutations, accounting for 12.2% (10/82) of the cases initially reported as not carrying actionable mutations. Therefore, comprehensive genomic profiling should be actively performed early in cases with high clinical suspicion of EGFR mutations.