Abstract 666: Developing an ascitic fluid-derived organoid model for transcriptomic and therapeutic investigations in ovarian cancer.

Abstract Introduction: Epithelial ovarian cancer (EOC) spreads freely within the intraperitoneal cavity, enabling tumor dissemination, abdominal organ adhesion, and ascites formation through lymphatic obstruction. Because solid-tumor samples are scarce after debulking surgery, ascites provide a crucial window into disease evolution. Its rich cellular and acellular components fuel tumor survival, immune evasion, and chemoresistance but remain underused in preclinical models. We therefore aim to establish and characterize an ascites-derived organoid (AsO) platform that captures this heterogeneous tumor microenvironment (TME) and improves drug-response profiling. Methods: Malignant ascites and tumor tissues were collected from consenting Hispanic patients under an approved IRB protocol. Ascitic fluid was centrifuged and repeatedly lysed to remove red blood cells. The whole ascitic cells (WhAs) were divided for organoid culture and biobanking. Part of WhAs was embedded in extracellular matrix and overlaid with optimized organoid culture media. Organoids were passaged every 8-13 days and cryopreserved in freezing media. We documented morphology with brightfield imaging, stained FFPE sections with H Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 666.