Osimertinib is a potent, irreversible EGFR tyrosine kinase inhibitor (TKI) selective for EGFR-TKI sensitizing (EGFRm) and T790M resistance mutations. The primary objective of the cytology cohort in the AURA study was to investigate safety and efficacy of osimertinib in pretreated Japanese patients with EGFR T790M mutation-positive NSCLC, with screening EGFR T790M mutation status determined from cytology samples. The cytology cohort was included in the Phase I dose expansion component of the AURA study. Patients were enrolled based on a positive result of T790M by using cytology samples, and received osimertinib 80 mg in tablet form once daily until disease progression or until clinical benefit was no longer observed at the discretion of the investigator. The primary endpoint for efficacy was objective response rate (ORR) by investigator assessment. Twenty-eight Japanese patients were enrolled into the cytology cohort. At data cut-off (1 February 2016), 12 (43%) were on treatment. Investigator-assessed ORR was 75% (95% CI 55, 89) and median duration of response was 9.7 months (95% CI 3.8, NC). Median progression-free survival was 8.3 months (95% CI 4.2, NC) and disease control rate 96% (95% CI 82, 100). The most common all-causality adverse events were paronychia (46%), dry skin (46%), diarrhea (36%) and rash (36%). Osimertinib provided clinical benefit with a manageable safety profile in patients with pretreated EGFR T790M mutation-positive NSCLC, whose screening EGFR T790M mutation positive status was determined from cytology samples. (ClinicalTrials. gov number NCT01802632.) This article is protected by copyright. All rights reserved.