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Abstract Peritoneal metastasis of pancreas cancer is one of the ultimate modes of spread in the cancer. Little is known about how cancer cells spread into abdominal cavity and what is different from hematogenous metastasis. It is also not well characterized how tumor microenvironment prevent cancer cells from spreading in abdominal cavity. We performed single-cell RNA-seq analysis and special transcriptomic analysis to clarify the progression and environment of the cancer. We collected and processed ascites samples of 20 PDAC samples from 19 patients. Sixteen ascites samples were obtained from abdominal paracentesis and two cases in the postmortem period. For one patient ascites was collected both pre and postmortem. All but one patient received chemotherapy prior to ascites collection. Routine clinical cytology evaluation of ascites samples from 17 patients indicated it was malignant in 11 patients and nonmalignant in six patients. All ascites samples were purified by gradient centrifuge using Ficoll-Paque Plus to remove erythrocytes and necrotic debris. For the platform, we adopted the 10x Genomics Chromium Single Cell Gene Expression platform for single-cell RNA-seq library preparation. Spatial transcriptomics was performed for eight FFPE samples from the two autopsy patients with paired cancer ascites using 10x Visium. The CytAssist was used to transfer transcripts of pre-sectioned and pre-stained tissues with 11 × 11 mm Visium Capture Area slides. The sample locations were metastatic tumors to bowel wall, rib bone, mesentery, iliac nerve, diaphragm, peritoneum, pelvis, and primary pancreas tumor. A total of 248, 263 cells were analyzed in single-cell RNA-seq. Cell population in pancreas cancer ascites consisted of macrophages, lymphocytes, dendritic cells, plasma cells, plasmacytoid dendritic cells, mesothelial cells, and cancer cells. Cancer cells were detected in twelve samples whereas no cancer cells were detected in eight samples. Gene ontology and gene set enrichment analyses showed macrophages in ascites with cancer cells involved neutrophil activation while those in ascites without cancer cells retained antigen presentation capacity and inducing interferon gamma pathway. Mesothelial cells in ascites with cancer cells showed more apoptosis and lymphocyte proliferation while those in ascites without cancers cells triggered fibrosis and mitosis. These data suggest that macrophage and mesothelial cells could be categorized into anti-tumor cells and tumor associated cells. Ongoing investigations are exploring ligand-receptor relationships. We are going to compare the expression profile of tumor cells in ascites fluid and in tissue from various organs by integrating single cell RNA-seq data and special transcriptomics data. Citation Format: Shigeaki Umeda, Elias-Ramzey Karnoub, Fiyinfolu Balogun, Alejandro Jiménez-Sánchez, Christine A. Iacobuzio-Donahue. Tumor progression and tumor microenvironment of pancreas cancer ascites revealed by scRNA-seq and spatial transcriptomics abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 1273.
Umeda et al. (Fri,) studied this question.