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Background: Epithelial ovarian cancer (EOC) remains a significant challenge in gynecologic oncology, particularly in the context of platinum-resistant disease. Mirvetuximab soravtansine (MIRV), was approved after trials revealed favorable response and survival outcomes. MIRV targets folate receptor alpha (FRα), a cell-surface receptor that is overexpressed in EOC and has been associated with aggressive disease phenotypes., Methods: This retrospective study analyzed 425 patient samples tested for FRα using the VENTANA® FOLR1 RxDx immunohistochemical assay. The patient cohort included cases with high grade serous carcinoma predominantly, tested across various anatomical sites. Statistical analysis examined the correlation between FRα positivity and clinical parameters such as tumor site and histology., Results: FRα was highly expressed in 36.3 % of the cases, with a significant association between FRα positivity and high grade serous ovarian histology. Tumor samples from the ovary, fallopian tube, adnexa, and dominant pelvic masses showed higher FRα positivity compared to metastatic sites (positive rates of 44.4 % vs 32.5 %, p = 0.02), highlighting the potential influence of tumor origin on expression of FRα. Time between sample collection and testing did not impact FRα expression, with sample testing spread over a median of 19.5 months post-collection. Eight patients had more than one specimen tested, of which 3 (37.5 %) had discordant results when a subsequent specimen was tested., Conclusion: Our results highlight a need for standardized protocols for FRα testing to ensure accurate biomarker evaluation across varied clinical settings. The heterogeneity in FRα expression, influenced by tumor histology and anatomical origin, warrant further investigation to optimize therapeutic outcomes., Prior Presentation: Preliminary findings from this study were previously presented in poster format at the Society of Gynecologic Oncology 2024 Annual Metting. We confirm that the submission complies with the journal requirements., Competing Interests: Declaration of competing interest This manuscript was funded by Labcorp. Rebecca A. Previs is a current employee of Labcorp, owns Labcorp stock, and receives travel support from Labcorp. Kyle C. Strickland is a current employee of Labcorp, owns Labcorp stock, and consulting fees from Foundation Medicine, Almac Pharmaceuticals, OncoQuest Pharmaceuticals, and CanariaBio. Zachary Wallen is a current employee of Labcorp, owns Labcorp stock, and receives travel support from Labcorp. Heidi Ko is a current employee of Labcorp and owns Labcorp stock. Michelle Green is a current employee of Labcorp. Maureen Cooper was a former employee of Labcorp and owns Labcorp stock. Elizabeth Lyon is a current employee of Labcorp and owns Labcorp stock. Michael Biorn is a current employee of Labcorp and owns Labcorp stock. Jennifer Armetta is a current employee of Labcorp and owns Labcorp stock. Rennie Quarles is a current employee of Labcorp and owns Labcorp stock. Catherine H Watson has no disclosures. Kari Ring received speakers' bureau honoraria from Ethicon. Jonathan L. Klein is a current employee of Labcorp and owns Labcorp stock. Brian Caveney is a board member of the Personalized Medicine Coalition, a current employee of Labcorp and owns Labcorp stock. Eric A. Severson is a current employee of Labcorp and owns Labcorp stock. Shakti Ramkissoon is a current employee of Labcorp and owns Labcorp stock., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)