Rete Ovarii Epithelial Cells as an Unappreciated Cell of Origin for Pelvic and Ovarian High-Grade Serous Carcinoma.

Over the past two decades, converging clinicopathologic, molecular, and evolutionary evidence has established that pelvic and ovarian high-grade serous carcinoma (HGSC) originates predominantly from tubal-type epithelia rather than the ovarian surface epithelium. Consequently, Fallopian tube secretory epithelial cells are widely recognized as the principal cell of origin for HGSC. However, the female reproductive tract contains additional tubular epithelial networks whose potential contributions to HGSC pathogenesis remain unexplored. Here, we identify the rete ovarii (RO), a complex network of intra- and extra-ovarian tubules located within the ovarian hilus and mesovarium, as an alternative candidate tissue of origin for HGSC. We demonstrate that genetic and genomic alterations in rete ovarii epithelial cells (ROECs) can drive their malignant transformation, giving rise to tumors that closely recapitulate the histologic and molecular characteristics of human HGSC. Spatially resolved single-cell transcriptomic analyses of tumors derived from Brca/Trp53/Pten-deficient ROECs (BTP-RO) reveal distinct invasive and immunosuppressive molecular programs. These findings establish ROECs as a previously unrecognized cell of origin for HGSC, expanding the landscape of potential precursor populations beyond the Fallopian tube. The RO-based HGSC model provides a powerful framework for developing origin-informed prevention strategies, early detection approaches, and targeted therapeutics.