Abstract
In this study, a patient with lung adenocarcinoma harboring an EGFR mutation exhibited primary resistance to the targeted EGFR inhibitor Osimertinib after 2 months of treatment. As the disease advanced, further genetic analysis revealed the emergence of additional mutations in ARID1A, NTRK1, and ZRSR2, alongside the existing EGFR mutation. Subsequent treatment with Pemetrexed resulted in a significant reduction in liver metastases. Protein mass spectrometry sequencing and immunohistochemical analysis collectively indicated that the PI3K/mTOR pathway mediates the mechanism through which these gene mutations confer primary drug resistance. Evidence demonstrates that the co-occurrence of EGFR and ARID1A mutations diminishes the efficacy of EGFR tyrosine kinase inhibitors (EGFR TKIs). Consequently, it is hypothesized that mutations in NTRK1 and ZRSR2, which are implicated in the PI3K/mTOR pathway, contribute to the primary resistance observed with Osimertinib treatment. In this case, the illness was effectively managed through prompt adjustments to the treatment regimen and the rapid administration of chemotherapy drugs. This finding also constitutes the first evidence that mutations in NTRK1 and ZRSR2 are pivotal in the development of primary resistance to Osimertinib. Consequently, it is imperative to conduct genetic testing at the earliest opportunity and modify the treatment plan accordingly.