LBA5515 Background: Batiraxcept is an Fc-fusion protein engineered to have a 200-fold higher affinity than wild-type AXL for its activating ligand GAS6. Batiraxcept sequesters GAS6 and inhibits its interaction with AXL. The Phase 1b study demonstrated safety with batiraxcept in combination with paclitaxel. Methods: This was a global, placebo-controlled, double-blind, phase III trial (ClinicalTrials.gov identifier: NCT04729608). Patients with PROC were randomly assigned 1:1 to receive intravenous batiraxcept every 2 weeks (D1, 15 every 28 days) with once-a-week IV paclitaxel (D1, 8, 15 every 28 days) or placebo with paclitaxel until disease progression. The primary endpoint was progression-free survival as assessed by investigator-assessed progression-free survival and secondary endpoint was overall survival. The randomization was stratified by platinum-free interval (< 3 months, 3 to 6 months), prior lines (1 to 2, 3 to 4), and prior bevacizumab status (yes, no). Exploratory endpoints include objective response rate, duration of response, quality of life, clinical benefit rate, and pharmacokinetic and pharmacodynamic profile. Results: A total of 366 participants were randomly assigned, and analysis was performed based on intent-to-treat. There were 183 participants who had prior bevacizumab and 177 with no prior bevacizumab. Median PFS (mPFS) was 5.13 months in the batiraxcept + paclitaxel arm and 5.49 months in the control paclitaxel arm, hazard ratio (HR) 1.29 (CI, 1.01 to 1.64; p=0.98). Median OS with batiraxcept + paclitaxel was 14.29 months versus 14.39 months, HR 1.06 (CI 0.77 to 1.46; p=0.64). Objective response rates (ORRs) per RECIST 1.1 were similar in both arms: 25.1% with batiraxcept + paclitaxel versus 26.2% with control paclitaxel arm. An exploratory analysis of the 304 evaluable tumors found that 61 (20%) of tumors had high AXL expression by immunohistochemistry (IHC). In participants with high tumor AXL expression, median PFS was 5.78 months in the batiraxcept + paclitaxel arm and 3.71 months in the control paclitaxel arm, HR 0.55 (CI, 0.31 to 0.98; p=0.042). For high AXL expressing tumors, median OS was 17.8 months in the batiraxcept + paclitaxel cohort and 8.11 months in the paclitaxel cohort, HR 0.32 (CI, 0.14 to 0.73; p=0.006). Conclusions: The addition of batiraxcept to paclitaxel did not improve PFS or OS. However, in AXL high tumors, the PFS and OS were higher in participants who received batiraxcept with paclitaxel compared to paclitaxel alone. Clinical trial information: NCT04729608 .