ECP 2022 Abstract Book

Virchows Archiv (2022) 481 (Suppl 1):S1–S364 13 stained slides of gastric and duodenal biopsies were reviewed and immunohistochemistry was performed. Results: 19/461 patients (4.1%) under treatment with ICIs were histologically confirmed with gastritis. 6/19 (31%) showed severe lesions of active gastritis on biopsies, while 13/19 (69%) showed mild/moderate gastritis. Histologically, all severe cases corresponded to diffuse chronic active gastritis involving the full thickness of the mucosa with different degrees of inf lammation between the antrum and fundus. Important neutrophilic infiltrate was present with crypt abscesses, intra-epithelial lymphocytosis CD8+ and massive gland destruction with interstitial CD4+ predominant T lymphocytes. Immunohistochemistry for CMV and Helicobacter Pylori was negative. Among the six cases with severe gastritis, four patients had a normal endoscopic appearance of gastric mucosa/ minor lesions and two patients showed gastric erosions/ulcerations. Conclusion: Severe damage in ICI-induced gastritis can be associ- ated with a normal endoscopic appearance. It is characterized by a chronic active gastritis pattern with abundant infiltration of mucosa and epithelium by lymphocytes and neutrophils and massive gland destruction. Despite a normal endoscopic appearance, biopsies of both fundus and antrum should be performed, as histology can be contrasting in different gastric regions. PS-07-016 Diagnostic usefulness of p53 immunostaining in gastric cancer and dysplasia: a real-world clinical experience M. Kim* *Kyungpook University Hospital, Republic of Korea Background & objectives: Stomach cancer are major threat to public health. A subset of gastric cancer harbour mutations of TP53. Gastric cancer with mutant TP53 gene usually accompanies morphologic changes. We have investigated the diagnostic utility of p53 immunostaining in real-world cases. Methods: We retrospectively searched 50 stomach tumour and tumour-like lesion cases, wherein p53 immunostaining had a pivotal role in the diagnosis. P53 staining pattern was also analysed in association with clinicopathologic parameters. Results: Mutant pattern p53 staining was significantly correlated with high-grade nuclear atypia (p<0.001), high-grade dysplasia and tubular adenocarcinoma (p<0.001), and MSS status (p=0.034). Furthermore, diagnostic application of p53 immunostaining was useful when 1) biopsy specimen contained only few tumour cells, 2) pathologic resection margin evaluation was difficult to due to the cauterization artifact 3) distinction of low-grade and high-grade gastric dysplasia. Conclusion: p53 immunostaining can be helpful for the diagnosis of gastric tumour and tumour-like lesions, and accurate pathologic margin evaluation, particularly if the lesion shows intestinal-type differentiation and some degree of nuclear atypia. PS-07-017 Tumour area infiltration and absolute tumour cell counts in endoscopic biopsies of therapy-naive upper GI tract carcinomas - implications for predictive biomarker testing A. Quaas*, H. Lamberty, A.H. Scheel, Y. Tolkach, F. Gebauer, B. Schoemig-Markiefka, T. Zander, R. Büttner, J. Rueschoff, C.J. Bruns, W. Schroeder * Institute of Pathology, University Hospital Cologne, Germany Background & objectives: Guidelines regulate how many biopsies should be taken to obtain reliable results of predictive biomarker tests. Little is known about how well these guidelines are applied, the number of biopsies correlates with the tumour area and the tumour cells counts. Methods: The study included endoscopic biopsies of untreated carcinomas of the upper gastrointestinal (GI)-tract during the 2015- 2020 review period. Archival (H&E)-stained histological sections were digitized, and the tumour areas were manually annotated. The tumour-bearing biopsy area and absolute carcinoma cell count per case were determined by image analysis. Results: Biopsies from 253 patients were analysed. The follow- ing mean values were determined: a) tumour biopsy number: 6.5 (1–25, standard deviation (SD)=3,32, b) number of tumour-bearing biopsies: 4.7 (1–19, SD=2,80), c) tumour infiltrated area: 7.4mm2 (0.19 mm2–59.46 mm2), d) absolute tumour cell count: 13,492 (193–92,834) e) tumour cell count in a primary surgical specimen (tumour size: 6.7 cm): 105,200,176. The guideline-recommended biopsy count of 10 was not achieved in 208 patients (82.2%), and the required tumour-bearing biopsy count of 5 was not achieved in 133 patients (52.6%). Conclusion: Biopsies are often used to determine predictive biomarkers, like Her2/neu or PD-L1. Diagnostics standards to ensure representative material have been suggested in guidelines to reduce false-negative predictions. This is the first study describing the relationships between biopsy number, actual infiltrated tumour area, and carcinoma cell number. We advocate, that histopathological reports should indicate on which basis statements on therapy-relevant biomarkers were made. Digital pathology has the potential to objectively capture these parameters for documentation, quality assessment, and future clinical studies. PS-07-018 Immune microenvironment landscape shows treatment spe- cific differences in rectal cancer patients C. Graham Martínez*, Y. Barella, S. Kus Oztürk, M. Gorris, S. van Lent-van Vliet, C.A. Marijnen, I. Nagtegaal *Radboud University Medical centre, The Netherlands Background & objectives: Neoadjuvant therapy is the backbone of modern rectal cancer treatment. Insight into the biology of tumour response is needed to optimize organ-preserving approaches. The aim of this study is to explore treatment-specific responses of the tumour and tumour microenvironment. Methods: Locally advanced rectal cancer patients were treated with chemotherapy (CT), radiochemotherapy (RCT), radiotherapy short wait (RTS) or long wait (LRT) or did not receive therapy (NT). 16 patients per group were included. Tumour patterns of response assessed on HE slides. IF-multiplex was performed for Tcyt (CD3+CD8+), Treg (CD3+FOXP3+), Thelper (CD3+CD8- FOXP3-), B cell (CD20+), DC (CD11c+) & Tumour (panCK+). Results: A fragmented pattern was predominant in CT-and-RCT- treated patients, whereas shrinkage pattern was predominant in LRT-treated patients (p=0.02). Thelper cells were the pre- dominant immune cell population across therapies and a higher immune cell density was observed in stroma compared to tumour region. The depletion of Tregs after therapy suggests a long and maybe permanent effect on the tumour microenvironment. Acute RT affects Tcyt infiltrate (p<0.01). Brachytherapy-treated patients show the lowest densities of stromal Thelper, Tcyt & Tregs (p <0.01). Synergistic effect of RCT induces stromal increase of Tcyt cells and depletion of Thelper cells compared to CT. All patients treated with some form of radiotherapy had a more homogeneous immune response. Conclusion: We demonstrated treatment-specific differences in the immune microenvironment landscape of RC patients. Local treatment including RT lead to a more homogeneous immune response compared to NT and CT. Understanding the immune S95