Clinical implications of the T790M mutation in disease characteristics and treatment response in patients with EGFR-mutated NSCLC.

Abstract

9031 Background: The secondary T790M mutation accounts for more than 50% of acquired tyrosine kinase inhibitor (TKI) resistance in epidermal growth factor receptor (EGFR)-mutant NSCLC patients. Recent reports suggest this resistance mutation may be more common among patients with longer progression-free survival (PFS) on first-line TKI therapy, but much is still unknown about this resistance mechanism’s association with response to other therapies. Methods: Our group collected medical records from patients who underwent a biopsy for T790M mutation testing in the process of screening for clinical trials involving third generation EGFR inhibitors. Medical records were retrospectively analyzed for demographic data, PFS, best response (BR) to previous therapies, and presence or absence of an acquired T790M mutation. Progression-free survival was estimated using the Kaplan-Meier method and compared across two groups using the log-ranked test followed by univariate and multivariate cox proportional hazard regression analysis. Response rates were compared using Fisher’s exact test. Results: Out of 102 patients who obtained a diagnostic biopsy, 73 patients had a T790M mutation. Patients who later developed a T790M mutation had a longer PFS on first-line TKI therapy (12.0 months in T790M+ vs. 8.0 months in T790M-, p = 0.038, HR 1.66, 95% CI 1.03-2.67), though there was no difference in response rate (75.5% in T790M+ vs 77.3% in T790M-, p = 1.00). T790M+ patients also had a longer PFS on initial chemotherapy treatment (5.0 months in T790M+ vs. 4.0 months in T790M-, p = 0.020, HR 1.97, 95% CI 1.11-3.49) and a higher response rate to chemotherapy (22.7% in T790M+ vs 0% in T790M-, p = 0.033). Median PFS was short (3.0 months) for patients treated with immunotherapy with no difference based on T790M mutation status (p = 0.33). Conclusions: Our study confirms that tumors expressing T790M have a more indolent progression of disease compared to their T790M negative counterparts when treated with both first-line TKI and cytotoxic chemotherapy. This data provides context for therapeutic decision making in EGFR-mutant NSCLC patients.