Introduction: The association between the response to first-line epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) and survival in EGFR mutation-positive non-small-cell lung cancer (NSCLC) remains unclear. We studied the association between the response to first-line EGFR-TKIs and survival using Response Evaluation Criteria In Solid Tumors (RECIST) and maximal tumor shrinkage.
Materials and methods: We analyzed data from patients with advanced EGFR mutation-positive NSCLC enrolled in first-line gefitinib and afatinib trials. A total of 98 patients who achieved a response or stable disease and had ≥ 1 measurable target lesion were included. The association between the best response by RECIST or maximal tumor shrinkage and survival was analyzed in Kaplan-Meier and Cox regression models with the landmark method. The specified landmark time points were 8 weeks, the median time to maximal tumor shrinkage (16.5 weeks), and median progression-free survival (PFS; 56 weeks).
Results: A total of 76 patients (77%) responded to gefitinib or afatinib. Of these 76 patients, 49 (64%) and 75 (99%) had achieved a response at 8 and 16.5 weeks, respectively. All responders had achieved a response by 56 weeks. The responders had a significantly longer PFS and overall survival (OS) compared with those with stable disease at 16.5 weeks (PFS, P = .003; OS, P < .001) and 56 weeks (PFS, P = .026; OS, P = .016) but not at 8 weeks (PFS, P = .104; OS, P = .313). Among the responders, greater tumor shrinkage was not associated with longer PFS or OS.
Conclusion: Those with a response to first-line gefitinib or afatinib had more favorable PFS and OS compared with those with stable disease. A sufficient observation period was required for the response to occur and predict outcomes. Greater maximal tumor shrinkage in the responders was not predictive of survival.
Keywords: Afatinib; Depth of response; EGFR mutation-positive NSCLC; Gefitinib.
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