Abstract Introduction: Ovarian carcinosarcoma (OCS) is a rare and deadly subtype of ovarian cancer, characterized by an admixture of epithelial and mesenchymal components. The limited understanding of its pathogenesis and the lack of effective therapies highlight the need for pre-clinical OCS models. In particular, the role of inflammation in OCS pathogenesis remains unknown. Methods: We generated an inducible genetically engineered mouse model of OCS by deleting relevant tumor suppressor genes, namely Trp53, Brca2 and Pten, in the ovarian surface epithelium and fallopian tube epithelium. To assess the role of NSAIDs in OCS, mice were treated with indomethacin starting shortly after tumor induction. We performed single-cell RNA sequencing (scRNA-seq) analysis of tumors and metastases and validated key findings using immunohistochemistry and flow cytometry. Finally, we created murine OCS cell lines and conducted an in vivo omentum migration assay and bulk RNA-seq, to distinguish the effects of NSAIDs on tumor cells versus the tumor microenvironment (TME). Results: Mice in our model developed ovarian tumors that recapitulated the dual epithelial-mesenchymal morphology of OCS and expressed clinically relevant OCS markers. Deletion of Trp53 and Pten was essential for tumor formation, whereas Brca2 deletion had only a minimal effect on survival. Tumors with combined Trp53, Brca2, and Pten deletion demonstrated high macrophage infiltration within the TME, mirroring human OCS and supporting the model’s suitability for investigating the role of inflammation in this disease. Indomethacin-treated mice developed markedly smaller primary tumors and exhibited prolonged survival, yet showed a significant increase in metastatic burden, highlighting the double-edged role of inflammation in OCS. scRNA-seq analysis revealed that indomethacin affected both cancer cells and the TME. Indomethacin-treated cancer cells expressed lower levels of genes associated with angiogenesis and extra cellular matrix turnover. Indomethacin led to a marked reduction in macrophages abundance within primary tumors, accompanied by decreased CD4 and CD8 T cells and an increase in T regulatory cells. An in vivo omentum migration assay demonstrated a metastasis-suppressing effect on the pre-metastatic niche, alongside a direct metastasis-enhancing effect on the tumor cells. Finally, bulk RNA-seq of mOCS cells treated with indomethacin revealed a dramatic upregulation of cholesterol homeostasis pathways, potentially mediating the pro-metastatic effect on cancer cells. Conclusions: We developed a reproducible OCS model that faithfully mirrors key pathological and molecular features of the human disease. While the tumor-suppressive effects of NSAIDs were discussed in other cancer types, we caution that NSAIDS might have contradictory and complex roles in specific tumor types. Citation Format: Einav Bangiev Girsh, Roba Gabesh, Eden Gal, Amir Basis, Sharona Tornovsky-Babeay, Gwo Yaw Ho, Dimitri Goncherovsky, Morad Zayoud, Paul Zannou, Inna Naroditsky, Tamar Klienberger, Liron Berger, Oren Parnas, Ruth Perets. The double-edged role of anti-inflammatory drugs in ovarian carcinosarcoma, in a Trp53;Brca2;Pten genetically engineered mouse model abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 6068.
Girsh et al. (Fri,) studied this question.