Abstract 5156: Is the formation of Stroma AReactive Invasion Front Areas in colorectal cancer driven by characteristic extracellular matrix reorganization processes based on the plasmin/plasminogen system
Authors: Grosser Bianca , Reitsam Nic G. , Sommer Florian , Hardt Jochen , Märkl Bruno 
Published: March 2024

Abstract
Background: As patient stratification still needs to be refined in colorectal cancer (CRC), we established SARIFA (Stroma AReactive Invasion Front Areas) as a novel H&E-based prognostic biomarker that is defined by a direct tumor-adipocyte interaction with a lack of desmoplastic reaction. Even though we could prove the high prognostic relevance of SARIFA now in multiple cohorts in gastric, colorectal, and pancreatic cancer, as well as could link an upregulation of lipid metabolism and immune alterations to this specific aggressive tumor biology, it remains an open question how SARIFAs are formed mechanistically.
Materials/Methods: Based on the results of our recently established SARIFA-scores in the TCGA-CRC (TCGA-COAD & TCGA-READ cohorts; SARIFA-positive n=69, SARIFA-negative n=138) and the corresponding differential gene expression analysis, which are part of a previous study, protein levels (in ng/mL) measured by commercially available uPA and PAI1 enzyme-linked immunosorbent assays (ELISAs) were compared between SARIFA-positive and SARIFA-negative CRC patients (SARIFA-positive n=35, SARIFA-negative n=62). Additionally, immunohistochemistry for FABP4 as a key player in lipid metabolism was performed. Moreover, spatial transcriptomics (digital spatial profiling, DSP) was performed with tumor and stroma section segmentation on a subset of cases.
Results: In TCGA-CRC, SERPINE1 (PAI1), as well as PLAU (uPA), are both significantly upregulated on mRNA level (LFC: 1.14 and 0.74, respectively; both adjusted p-values ≤0.001). Logically, SERPINE1 and PLAU are highly expressed in mesenchymal CMS4 CRCs, which overlap with SARIFA-positivity. This is reflected by an upregulation of matrix metalloproteinases in predicted functional protein networks (STRING analysis). In our local cohort, we could now validate this upregulation of uPA in SARIFA-positive CRCs on protein level (p=0.0027). For PAI1, a trend towards higher protein levels in SARIFA-positive CRCs could be observed (p=0.209). Moreover, SARIFA-positive CRCs show a higher number of tumor buds (p=0.013) as well as increased FABP4 expression at the invasion front (p&lt;0.001) in our local cohort. In DSP analysis, the stroma fraction of SARIFA-positive CRCs showed significant changes compared to SARIFA-negative cases.
Conclusion: Our current data shows that the formation of SARIFAs and the consecutive direct tumor-adipocyte interaction with a tumor-promoting increase in lipid metabolism may rely on alterations in the plasmin/plasminogen system, which could be a novel potential drug target in the aggressive subset of SARIFA-positive CRCs.
Citation Format: Bianca Grosser, Nic G. Reitsam, Florian Sommer, Jochen Hardt, Bruno Märkl. Is the formation of Stroma AReactive Invasion Front Areas in colorectal cancer driven by characteristic extracellular matrix reorganization processes based on the plasmin/plasminogen system [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 5156.