The study will be conducted in approximately 5 sites across South Korea and will include EGFR TKI pre-treated patients. All patients will be required to have NSCLC associated with at least 1 site of LM as identified by the Investigator that can be assessed by magnetic resonance imaging (MRI) scan and that is suitable for repeat assessments. Presence of Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST 1.1) measurable intracranial (INC) metastases (ie, brain parenchyma and cranial leptomeninges) and/or extracranial (EXC) metastases is not mandatory. The presence of LM will be based on the Investigator assessment of the brain MRI scan. LM will be confirmed by radiologist from the central site to ensure that patients enrolled in the study are assessable for LM radiologically. Patients negative for LM according to radiologist assessment but enrolled in the study will be replaced. The replaced patient will be included in the study and will receive investigational product (IP) if, in the opinion of the Investigator, the patient is able to receive clinical benefit. Such a patient will not be evaluable for LM response in the LM-EFR analysis set.Full analyses set (FAS) is defined as patients enrolled who received at least 1 dose of study treatment. In addition to Response Assessment in Neuro-Oncology criteria for Leptomeningeal Metastases (RANO-LM) assessments, separate RECIST 1.1 imaging assessments on EXC disease and INC (both LM and non-LM) disease will be performed on images acquired using the preferred method of contrast-enhanced computed tomography (CT) scan of the chest and abdomen (and pelvis when indicated) (EXC) and gadolinium contrast-enhanced MRI scan of the brain (INC).~Baseline scans will be acquired within 28 days prior to first dose of IP and then every 8 weeks (±1 week) and every 12 weeks (±1 week) after 12 months relative to first dose. Patients who discontinue IP for reasons other than objective disease progression in all of INC, EXC, and LM, will continue scans every 8 weeks (±1 week; relative to date of first dose of IP) and every 12 weeks (±1 week, after 12 months) until objective progression in INC, EXC, and LM or withdrawal of consent. Progression refers to progression assessed objectively by imaging using RECIST 1.1 for non-LM INC and EXC or RANO-LM criteria as appropriate. If a patient has been deemed to have LM subjective disease progression according to radiological and clinical assessment by the Investigatorstudy treatment can be continue, and the patient should maintain tumor imaging assessments according to the schedule of assessments.~CSF sampling for cytology is not mandatory, but is strongly encouraged, in patients who are willing to have lumbar punctures during the study, or in those patients who have Ommaya reservoirs.~Physical examination, Eastern Cooperative Oncology Group (ECOG)/World Health Organization (WHO) performance status score, vital signs, and laboratory tests (hematology, clinical chemistry, and urinalysis) will be conducted at each visit. Adverse events (AEs) will be monitored and recorded on an ongoing basis. Twelve-lead electrocardiograms (ECGs) will be performed at baseline and at the time point of investigator's decision and will include measurement of the QT interval. A multigated acquisition scan (MUGA) or echocardiogram will be performed at baseline and at the time point of investigator's decision for left ventricular ejection fraction (LVEF) measurement. Plasma and CSF (if feasible) samples for pharmacokinetic (PK) analysis will be collected at pre-dose on Cycle 3 Day 1 and Cycle 6 Day 1.~Patient-Reported Outcome (PRO) questionnaires, including European Organization for Research and Treatment of Cancer (EORTC) Quality of Life Questionnaire-Core 30 items (EORTC QLQ-C30), EORTC Quality of Life Questionnaire-Brain Cancer Module 20 items (EORTC QLQ-BN20) will be collected at baseline (prior to first dose of IP and prior to all other assessments on Cycle 1 Day 1) and at home (every 8 weeks [±3 days for EORTC QLQ-C30 and EORTC QLQ-BN20 relative to administration of IP). The patient is asked to report PROs up to the end of Cycle 8 or to IP discontinuation, whichever comes first.
This will be a Phase II, open-label, single-arm, multicenter study of the efficacy and safety of osimertinib (80 mg orally once daily) in patients with LM associated with EGFRm+ NSCLC.