Efficacy and safety of first-generation epidermal growth factor receptor tyrosine kinase inhibitors in retreatment of patients without T790M

Patients receiving first-line epidermal growth factor receptor tyrosine kinase inhibitor (EGFR TKI) and undergoing second and/or third-line cytotoxic chemotherapy may experience regrowth of EGFR (+) clones. Retreatment with EGFR TKIs can provide antitumor effects and potentially induce T790M-positive conversion. This study evaluated the efficacy, safety, and T790M (+) conversion rates in patients without T790M mutation at the second biopsy retreated with first-generation EGFR TKIs as third-line or subsequent therapy. This open-label, multi-center, prospective phase II trial (NCT03382795) enrolled patients with non-small cell lung cancer (NSCLC) previously treated with first- or second-generation EGFR TKIs and cytotoxic chemotherapy They were retreated with gefitinib or erlotinib. Key endpoints included objective response rate (ORR), progression-free survival (PFS), overall survival (OS), and safety. Among 63 patients (34 on gefitinib, 29 on erlotinib), ORR was 14.3%. Median PFS was 2.2 months, and median OS was 8.6 months. Adverse events occurred in 82.5% of patients, primarily grade ≤2. The T790M conversion rate was 31.7% and was significantly associated with prior EGFR TKI exposure duration (P=0.047). Patients with T790M conversion had a median OS of 29.3 months, significantly (P<0.001) longer than the median OS of 6.0 months for non-converters. Next-generation sequencing (NGS) of pre-retreatment blood samples identified additional T790M mutations (20.8%) undetected by conventional testing. Low TP53 expression showed a non-significant trend toward higher tendency T790M conversion (66.7% vs. 30.8%, P=0.32). EGFR retreatment induced T790M conversion in 32% of cases, enabling third-generation EGFR TKIs, leading to a substantial improvement in median OS. Blood-based NGS identified additional T790M mutations, undetected by routine polymerase chain reaction (PCR). EGFR TKI retreatment with blood-based NGS may enhance patient prognosis by identifying additional T790M positive mutations.