Abstract 5480: Single cell and spatial transcriptomic profile of appendiceal tumour peritoneal disease
Authors: Strach Madeleine C. , Yeung Nicole , Apostolov Eva , Wang Tony , Lin Hui-Ming , Ansari Nabila , Koh Cherry , Shin Joo-Shik , Kench James , Swarbrick Alexander , Horvath Lisa , Mahon Kate L. 
Published: March 2024

Abstract
Introduction: Appendiceal tumors (AT) are rare and often develop peritoneal disease (PD), with 5 year survival of 15-63% for high grade adenocarcinomas (HG) and 46-96% for low grade mucinous neoplasms (LG). While the mainstay of treatment is cytoreductive surgery and heated intraperitoneal chemotherapy (CRS/HIPEC), the role of systemic chemotherapy is less clear with limited biological characterization of AT and its tumor microenvironment (TME). The purpose of this study was to evaluate the TME of AT PD. Here we present an atlas of AT PD cells alongside a spatially resolved transcriptomic profile comparing HG and LG.
Methods: We collected tissue from 29 patients with AT PD during CRS prior to HIPEC (18 LG, nine HG and two no tumor control). We performed comprehensive single-cell RNA sequencing (38224 cells) on fresh tissue specimens from nine patients (four HG, five LG), and whole transcriptome spatial analysis (&gt;18000 genes) using the GeoMx Digital Spatial Profiler on formalin-fixed paraffin-embedded tissue from 22 patients (five HG, 13 LG). In the spatial profiling, we used anti-CK20, anti-CD45 and SYTO 83 as morphology markers to select areas of interest (AOIs): tumor (CK20), immune (CD45) and stroma (non-CK20/CD45). Analyses were performed with R and a false discovery rate threshold of 0.05.
Results: Single-cell RNA sequencing showed that both LG and HG have a preponderance of T-lineage cells including CD8, CD4 and NK T-cells. Both LG and HG tumors display association of mesothelial cells with cancer-associated fibroblasts (CAF), and CAF subsets expressing genes of epithelial-mesenchymal transition (EMT). LG and HG tumors display different patterns of mucin gene expression - epithelial cells of HG express the secreted mucin MUC20 in addition to MUC2 and MUC5B also expressed in LG; a subset of mesothelial cells in LG but not HG express the transmembrane mucin genes MUC1, MUC3A, MUC12 and MUC16. Spatial analysis of tumor AOIs revealed HG compared to LG had increased expression of genes associated with MYC targets, oxidative phosphorylation, anti-tumor immune pathways (IFNα/γ response, intestinal immune network for IGA production), cell cycle pathways (E2F targets, G2M checkpoint) and EMT. LG compared to HG had increased expression of genes associated with inflammation-mediated disease (TNFα signaling via NFKB, inflammatory response), regulation of tumor growth (P53), hypoxia and early cell cycle (estrogen response) and glycosylation pathways. Immune and stromal AOIs did not have significant transcriptomic differences between LG and HG.
Conclusion: This study provides novel insights into the biological profile of AT PD by describing TME cell types, immune function, tumor growth and cell cycle pathways. These findings may be used to identify clinically relevant biomarkers and new therapeutic targets.
Citation Format: Madeleine C. Strach, Nicole Yeung, Eva Apostolov, Tony Wang, Hui-Ming Lin, Nabila Ansari, Cherry Koh, Joo-Shik Shin, James Kench, Alexander Swarbrick, Lisa Horvath, Kate L. Mahon. Single cell and spatial transcriptomic profile of appendiceal tumour peritoneal disease [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(6_Suppl):Abstract nr 5480.