Impact of tumor programmed death ligand-1 expression on osimertinib efficacy in untreated EGFR -mutated advanced non-small cell lung cancer: a prospective observational study

Osimertinib monotherapy is currently the standard of care as a first-line treatment for patients harboring ( ) mutations; however, some -mutated non-small cell lung cancer (NSCLC) patients exhibit primary resistance and an insufficient response to EGFR-tyrosine kinase inhibitors (EGFR-TKIs). Elevated programmed death-ligand 1 (PD-L1) expression in tumors was reported as a negative predictive factor for outcomes of first- or second-generation EGFR-TKIs. We prospectively assessed advanced NSCLC patients with mutations who were treated with osimertinib at 14 institutions in Japan between September 2019 and December 2020. Relationships between outcomes of osimertinib monotherapy and patients' characteristics were reviewed. Seventy-one patients who underwent the tumor PD-L1 test were enrolled. Multivariate analysis identified tumor PD-L1 expression as an independent predictor for progression-free survival (PFS) with osimertinib treatment (P=0.029). The objective-response and disease-control rates for osimertinib treatment were significantly lower in patients demonstrating elevated PD-L1 levels relative to those with low or negative PD-L1 level (P=0.043 and P=0.007, respectively). Furthermore, among patients treated with osimertinib, those with high PD-L1 levels exhibited shorter PFS relative to those with low plus negative PD-L1 level (median PFS: 5.0 17.4 months; P