Abstract 2429: Tumor and stromal AXL expression regulate ovarian cancer metastasis
Authors: Mullen Mary Margaret , van Biljon Lillian N. , Quinn Jeanne , Greenwade Molly , Opara Gregory , Noia Hollie , Hagemann Ian S. , Hagemann Andrea R. , Kuroki Lindsay M. , McCourt Carolyn K. , Thaker Premal H. , Powell Matthew A. , Mutch David G. , Khabele Dineo , Fuh Katherine C. 
Published: June 2022

Abstract
Objective: Over 75% of patients with ovarian cancer present with widely metastatic disease. We have previously published that AXL is highly expressed in primary ovarian cancer tumors. However, it is unknown whether AXL expression in metastatic tumors correlates with outcome. Additionally, the role of stromally expressed AXL in metastasis has not been fully evaluated. Thus, the objective of this study is to evaluate the role of tumor and stromal AXL in the key steps of tumor metastasis.
Methods: Immunohistochemistry was used to measure AXL expression in a tissue microarray with primary and metastatic high grade ovarian tumors. Attachment assays as well as transwell and spheroid invasion assays were performed on established ovarian cancer cell lines. Mesothelial cell clearance assays utilizing human omentum-cultured mesothelial cells (HPMC) and additional invasion assays utilizing normal omental fibroblasts (NOF) were performed.
Results: 214 tumor samples were included from 139 patients: 122 primary and 92 metastatic sites, contributing to 85 matched samples. Most had high-grade serous histology (79%) and stage III-IV disease (79%). High AXL expression in metastatic tumors was associated with decreased overall survival (HRadj 1.8, 95% CI 1.03-3.1), but expression in primary tumors was not (1.1, 0.61-2.0). High vs. low AXL expression in metastases was associated with a decreased platinum-free interval (5.92 vs 15.9 months, P=0.03) and decreased progression-free survival (11.6 vs 18.8 months, P=0.02).Tumor AXL expression correlated with stromal AXL expression (R2=0.50, P&lt;0.001). Human ovarian tumor cells depleted of AXL had decreased attachment (OVCAR3-TPMES, 0.55-fold decrease P&lt;0.001) and invasion in transwell (OVCAR5, 173 vs 262 invasive tumor cells/hpf, P&lt;0.01) and spheroid (ES2, 87% vs 31% area invaded, P&lt;0.0001) invasion assays. Human ovarian cancer cells plated on AXL-deficient HPMCs had less cell clearance than those plated on AXL-expressing HPMCs (ES2, 6.0 vs 3.9 normalized area cleared, P&lt;0.001). Further, human ovarian cancer cells plated on AXL-deficient NOFs had less invasion than tumor cells plated on AXL expressing NOFs (OVCAR5, 173 vs 262 invasive tumor cells/hpf, P&lt;0.01).
Conclusions: High AXL expression in metastatic ovarian cancer cells correlates with worse survival and worse response to chemotherapy. Further, AXL expression in both tumor and stromal cells contributes to the steps of ovarian cancer metastasis.
Citation Format: Mary Margaret Mullen, Lillian N. van Biljon, Jeanne Quinn, Molly Greenwade, Gregory Opara, Hollie Noia, Ian S. Hagemann, Andrea R. Hagemann, Lindsay M. Kuroki, Carolyn K. McCourt, Premal H. Thaker, Matthew A. Powell, David G. Mutch, Dineo Khabele, Katherine C. Fuh. Tumor and stromal AXL expression regulate ovarian cancer metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2429.