TPS9154 Background: The combination of platinum, pemetrexed, and pembrolizumab (CIT) has become the standard of care in 1L non–oncogene addicted NSCLC. Despite an initial improvement in response rate and survival, the 5-year survival of NSCLC remains approximately 20-30%, due to the emergence of primary and acquired resistance. Additionally, the presence of brain metastases occurs in ˜30-50% of NSCLC patients and confers a poor prognosis. Among the currently non-actionable mutations, STK11/LKB1 mutations (STK11m) are common (˜20%) in NSCLC. Recent evidence suggests that STK11m NSCLC patients have a minimal response to checkpoint inhibitors and to chemo-immunotherapy in the first line setting. STK11m tumors are characterized by an immune-suppressed phenotype which is highly associated with AXL signalling. BEM, a first-in-class, oral, selective AXL inhibitor, has demonstrated the ability to prevent chemoresistance, re-sensitize STK11m NSCLC tumors to pembrolizumab, and enhance efficacy of CIT in preclinical lung models. Moreover, following oral administration, BEM readily distributes in brain tumour tissue in recurrent glioblastoma patients, with a 25.9 mean ratio of drug concentration in brain tissue to plasma. Therefore, the addition of BEM to CIT has the potential to improve 1L treatment outcomes in NSCLC overall and particularly in STK11m tumors. Methods: This is an open-label, multi-center, phase 1b/2a study to assess the safety, tolerability, and preliminary anti-tumor activity of BEM + CIT as 1L treatment in patients with advanced (Stage IIIb/IIIc) or metastatic (Stage IV) non-squamous NSCLC without actionable mutations. Patients with stable brain metastases are eligible to participate. Phase 1b follows a 3+3 design and will explore CIT in combination with one of 3 BEM dose levels: Cohort 1 = 75mg; Cohort 2 = 100 mg; or Cohort 3 = 150 mg. BEM is administered orally once/day on Day 1 of each 21-day treatment cycle. After 4 cycles of CIT + BEM, maintenance with BEM + pemetrexed + pembrolizumab is administered for up to 2 years. An independent data safety monitoring board will assess the safety data at the end of the dose-limiting toxicity period (the first 21 days of treatment for each patient, i.e. cycle 1) of each cohort and will recommend the BEM dose for the phase 2a expansion. In the phase 2a, up to 40 patients harboring a STK11m (regardless of their co-mutational status), in the absence of driver mutations will be enrolled. The study will include extensive co-mutational analyses via next-generation sequencing to identify potential sub-groups of patients deriving particular benefit. The trial is open to patient enrolment in phase1b in the US; recruitment for phase 2a is planned to open in Q2 2023 in Europe and US. EudraCT 2019‐003806‐28/NA/124645. Clinical trial information: NCT05469178 .