Background: In the Phase III FLAURA trial (NCT02296125), osimertinib, a third generation EGFR-TKI, showed superior efficacy to comparator EGFR-TKIs as first line treatment for EGFR mutation-positive (EGFRm) advanced NSCLC. In an exploratory analysis, we investigated clinical outcomes associated with detection of plasma EGFRm at 3 or 6 weeks (wks) after start of treatment. Methods: Treatment-naïve patients (pts) with EGFRm (ex19del or L858R) locally advanced or metastatic NSCLC were randomized 1:1 to receive osimertinib 80 mg once daily (QD) or comparator EGFR-TKIs (gefitinib 250 mg QD or erlotinib 150 mg QD). Plasma EGFR mutation analysis was conducted at baseline (BL), wks 3 and 6 by droplet digital PCR. Clearance was defined as undetectable levels of EGFRm in ctDNA at wks 3/6, where they were detectable at BL. Progression-free survival (PFS) was investigated based on early clearance of EGFRm. Results: In total 489/556 (88%) pts (osimertinib: 244/279; comparator: 245/277) had evaluable ctDNA at BL and wks 3/6. Of these, 342/489 (70%; osimertinib: 168/244; comparator: 174/245) had detectable BL EGFRm and were included in this analysis. See table. Conclusions: Clearance of plasma EGFRm after 3/6 wks of EGFR-TKI therapy was associated with a numerical improvement in PFS. The efficacy of osimertinib was superior to comparator EGFR-TKIs regardless of clearance status. Clinical trial information: NCT02296125

CI, confidence interval; D, detectable; HR, hazard ratio; mo, months; mPFS, median PFS; NC, non-calculable; ND, non-detectable