Abstract 760: Cell type resolved spatial proteomics defines the transition of precancerous fallopian tube lesions to invasive ovarian cancer

Serous epithelial ovarian cancer is the most common subtype of ovarian cancer, and it is thought to arise from dysplastic fallopian tube (FT) lesions. Depending on their histopathological characteristics and proliferative potential, precancerous lesions of the FT are categorized as p53 signatures, Serous Tubal Intraepithelial Lesions (STILs) or Serous Tubal Intraepithelial Carcinomas (STICs). In this study, we analyzed protein changes from precancerous lesions through invasive tumor development and metastasis to identify early molecular switches and druggable proteins for ovarian cancer treatment.We assembled a cohort of 5 p53 signatures, 8 STILs, 5 STICs alone, and 7 STICs with concurrent HGSC and 4 matching omental metastases. We interrogated these samples using Deep Visual Proteomics, an innovative technology we recently developed for spatial and cell-type resolved mass spectrometry-based proteomics. Epithelial cells were segmented using deep learning and classified into normal, dysplastic precursor, tumor, and metastasis. We collected 100-150 cell epithelial cell shapes for each pathologic category and 250 cell shape equivalents of adjacent stroma using laser capture microdissection. The samples were analyzed on a Thermo Orbitrap Astral mass spectrometer coupled to an Evosep One.Single injections of epithelial samples yielded a median of 6,562 proteins. The epithelial proteomics data validated that the secretory, and not the ciliated, epithelial FT cells are the origin of dysplastic FT lesions. While p53 signatures have at least 12 consecutively mutated cells lining the FT, they are almost identical to normal cells on the proteomic level. However, more than 2,000 proteins are differentially regulated in STIC vs normal secretory cells. Among these proteins, MARCKSL1 (cell motility and adhesion), WLS (Wnt signaling and cell proliferation), and PCNA (DNA repair and replication) are significantly enriched in STIC. In the stroma, we detected a median of 5,072 proteins. Interestingly, the PCA plot for components 1 and 2 reveals that separating STICs, invasive tumors, and omental metastases is better accomplished using the stroma than the epithelium. Consistent with the epithelial data, the transition from normal to the histologic p53 signature stroma is not accompanied by any proteomic changes in our dataset. However, STIC stroma, when compared to normal, is characterized by a significant loss of most collagens but not COL8, which shows the opposite trend. A massive extracellular matrix (ECM) remodeling is observed in the entire STIC tumor microenvironment, with significant regulation of ECM proteins like VCAN and laminins. In conclusion, our study provides a deep, cell-type resolved proteomics map of the transition of early FT lesions to invasive cancer and omental metastasis and identifies proteins with potential therapeutic or diagnostic implications. Citation Format: Andreas Metousis, Hilary Kenny, Lisa Schweizer, Agnes Bilecz, Rahul Krishnan, Isabel Alcazar, Mallika Ravi, Aasa Shimizu, Sophia Steigerwald, Thierry Nordmann, Ricardo Lastra, Ernst Lengyel, Matthias Mann. Cell type resolved spatial proteomics defines the transition of precancerous fallopian tube lesions to invasive ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 760.