ECP 2023 Abstracts

S2 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 Background & objectives: DR pattern is a novel prognostic factor in colorectal cancer (CRC) and CAFs derived from intra-tumorous lesion generating the “Immature” pattern, an independent poor prognostic histopathological feature of CRC patients, are shown to behave in a pro-tumour manner. Methods: CAFs were isolated and cultured from resected tumour’s tissue with “Mature” pattern (CAF-A) or that with “Immature” pat- tern (CAF-C) and exosomes released from CAFs were collected with the ultracentrifugation method. After confirming the exosomal proteins levels being sufficient by silver staining, the expression of programmed cell death ligand 1 on exosomes (PD-L1Ex) were also evaluated by western blotting. Results: In a total of 22 cases (CAF-A, 11; CAF-C, 11), all of CD9, an exosomal surface antigen, or exosome-derived miRNAs were successfully detected in exosome derived from CAFs. The total protein level of exosomes evaluated with a microvolume spectro- photometer was significantly higher in CAF-C (40.5 ng/ul) than in CAF-A (17.7ng/ul) (p=0.024; Welch test). Among 10 cases with sufficient exosomal proteins (5 CAF-A cases and 5 CAF-C cases, respectively), the expression of PD-L1Ex was identified in 2 cases, both of which were from the CAF-C exosomes and none of the 5 cases of CAF-A had PD-L1Ex. Conclusion: We reported previously that immature DR pattern was significantly relevant to the suppressed CD8+ T-cell infiltration, suggesting the pivotal association between fibrotic stromal envi- ronment and immune escape of tumour cells. Recently, exosomes derived from tumour cells, including PD-L1Ex, have intensively been investigated, however, exosomes derived from CAFs could also effectively induce immune escape of a tumour. The present study suggested that PD-L1Ex might be a factor contributing to the development of immune escape in the “Immature” DR environ- ment of CRC. OFP-01-004 NTRK gene alterations are enriched in gastric cancer with hepatoid differentiation but not in those with DNA mismatch repair protein deficiency Y. Fu*, X. Pu, X. Fan *Department of Pathology, Affiliated Drum Tower Hospital, Medical School of Nanjing University, China Background & objectives: Gastric cancer is a heterogeneous disease, and identifying the molecular characteristics of specific subtypes can aid in the development of targeted therapies. In this study, we aimed to investigate the clinicopathologic profile of gastric cancer with onco- genic NTRK alterations. Methods: We used NTRK break-apart probes and gene-specific probes for fluorescence in situ hybridization (FISH) to screen for NTRK fusion and amplification in 491 gastric cancer cases. We also collected additional samples from duodenal adenocarcinomas, endo- metrioid carcinomas, and colorectal cancers with dMMR to investigate the relationship between NTRK alterations and DNA MMR proteins. Results: Our analysis revealed that only four cases had NTRK alter- ations, including two cases with NTRK fusions and two cases with NTRK amplifications. Interestingly, all four cases were enriched in a specific subtype of gastric cancer, hepatoid adenocarcinomas of the stomach, and were all adenocarcinomas with enteroblastic differentiation. Furthermore, our analysis revealed that all five cases with NTRK gene fusions were found exclusively in colorec- tal cancer with dMMR. We also identified seven genes that were highly expressed in all three groups: CACNA1A, FGF18, BMP7, CHRNA7, CCKAR, BIRC3, and CXCL6. FGF18 and BMP7 in par- ticular may play a role in the interaction between the MMR system and NTRK gene alterations in HAS. Conclusion: Our study provides valuable insights into the molecular characteristics of gastric cancer with NTRK alterations. Our findings suggest that NTRK gene alterations are enriched in a specific sub- type of gastric cancer, HAS, and are not enriched in gastric cancer with dMMR. Furthermore, we identified common genes that may be involved in the interaction between the MMR system and NTRK gene alterations in HAS. These results may have important implications for the development of targeted therapies for gastric cancer. OFP-01-005 What is the value of lymph node regression after neoadjuvant chemoradiotherapy in rectal cancer? S. Kus Ozturk*, C. Graham Martinez, K. Verhoef, M. Tosetto, K. Sheahan, G.A. Hospers, C. van de Velde, C.A. Marijnen, C.S. van der Post, I. Nagtegaal *Radboud University Medical Centre (Radboudumc), The Netherlands Background & objectives: Following neoadjuvant therapy, regression may also be seen in lymph nodes and affect nodal stage. Our aim is to determine the role of regression of lymph nodes on outcome in patients with rectal cancer. Methods: All the lymph node slides were evaluated for metastasis (ypN) and regression (REG) (fibrosis and acellular mucin) in a cohort of 469 rectal cancer patients following chemoradiotherapy. According to ypN and REG status, a three-tiered (ypN0 REG+, ypN0 REG-, ypN+) and a four-tiered (ypN0 REG+, ypN0 REG-, ypN+ REG+, ypN+ REG-) classifications were generated and subgroups compared to each other. Results: In our cohort, the distribution of ypN0 REG+, ypN0 REG-, ypN+ REG+ and ypN+ REG- was 20%, 49%, 15%, and 16%, respec- tively. We found significantly better overall survival in ypN0 REG+ and worse overall survival in ypN+ group in both three-tiered (p=0.002) and four-tiered classifications (p=0.005). ypN0 REG+ group remained as the best prognostic group in DFS (three-tiered; p=0.004, four-tiered; p=0.01) and even outperformed ypN0 REG- group (p=0.008). Conclusion: Regression in lymph nodes is frequent and results in sig- nificantly better outcome compared to patients with remaining lymph node metastases. OFP-01-006 Intratumoral budding assessment in biopsies supports the preop- erative management of colorectal cancer patients S. Kus Ozturk*, J. Bokhorst, K. Sheahan, M. Vieth, A. Lugli, I. Nagtegaal *Radboud University Medical Centre (Radboudumc), The Netherlands Background & objectives: We aim to define the sufficiency crite- ria of a biopsy for an effective intratumoral budding (ITB) evalua- tion by using AI. We focus on the characteristics of the biopsy and its representation of tumour budding (TB) in the whole tumour. Methods: We examined the biopsy and corresponding resection speci- mens of 571 CRC patients. A tissue segmentation algorithm was used to quantify the amount of biopsy, tumour, and necrosis in biopsy mate- rials. The TBs were evaluated with an AI algorithm in H&E stained biopsy and resection slides. TB distribution was investigated within the first five millimetres from the lumen in 30 resections. Results: The average biopsy size, tumour, and necrosis were 71mm2, 7mm2, and 2mm2, respectively. Our preliminary analyses (n = 175) showed an increased gap between TB counts in biopsies and resections with smaller amounts of tumour in biopsies (rho= -0.13, p=0.07). The difference disappeared in biopsies with over 12 mm2 tumour. Within 1 mm from the tumour surface, 87% of the resections already contained TBs. ITB scores within five millimetres from the surface