Abstract
BACKGROUND: Not all non-small cell lung cancer (NSCLC) patients harboring epidermal growth factor receptor (EGFR) mutations respond equally to therapy with tyrosine kinase inhibitors (TKIs). Programmed death ligand-1 (PD-L1) has previously been speculated as a possible biomarker for treatment outcome because of its positive correlation with these mutations in cell lines, but clinical studies have yielded conflicting results. We investigate the predictive potential of this surface protein in relation to clinical benefit in patients as measured by time to treatment discontinuation (TTD). METHODS: We screened 516 Danish patients with EGFR mutations for inclusion based on a history of TKI treatment and a PD-L1 status that was assessed no earlier than three months prior to treatment initiation. Patients were stratified according to their expression of the potential biomarker as either negative (0%), low (1-49%) or high (≥50%). We employed the Kaplan-Meier method and the log rank test to test for a difference in treatment duration according to PD-L1 expression. RESULTS: We included 111 Danish patients. The median follow-up time from inclusion until death or censoring at the end of the study was 670 days (range, 32-1,664 days, 95% CI: 502-897 days). Fifty-seven patients (51%) categorized as PD-L1 expression negative, 32 (29%) as low and 22 (20%) as high. We tested for differences in treatment duration between the three groups. Our tests did not yield statistically significant P values. CONCLUSIONS: In our cohort of 111 Danish patients with NSCLC harboring mutations in the epidermal growth factor receptor gene, expression levels of PD-L1 did not significantly impact the duration of clinical benefit from tyrosine kinase treatment.