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Background: Treatment of advanced non-small cell lung cancer (NSCLC) with epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKIs) has a higher response rate than with conventional chemotherapy in patients positive for EGFR mutations. However, the efficacy of EGFR-TKI therapy may be reduced in patients positive for the EGFR exon 21 L858R point mutation., Objective: To determine the clinical characteristics of patients with EGFR exon 21 L858R point mutation-positive NSCLC who are non-responders to EGFR-TKI therapy and the factors that predict response to EGFR-TKI therapy., Methods: Patients with NSCLC treated with EGFR-TKIs were evaluated for response after treatment, and those who responded were compared with those who did not respond., Results: Of 31 patients, 21 (67.7%) responded to EGFR-TKI therapy (the response group). There were significantly more programmed death ligand 1 (PDL1)-negative patients in the response group than in the non-response group. A significantly higher number of patients in the PDL1-positive group developed interstitial lung disease (ILD) after EGFR-TKI therapy than those in the PDL1-negative group., Conclusion: EGFR-TKI therapy is likely to be non-responsive in PDL1-positive patients with EGFR exon 21 L858R point mutation-positive NSCLC. The PDL1-positive group is at a high risk of developing ILD., Competing Interests: Human subjects: Consent was obtained or waived by all participants in this study. Institutional Review Board of Kanazawa Medical University issued approval C057. This study was approved by the Institutional Review Board of Kanazawa Medical University (approval number: C057). Animal subjects: All authors have confirmed that this study did not involve animal subjects or tissue. Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work., (Copyright © 2024, Takahara et al.)