ECP 2023 Abstracts

S305 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 Conclusion: Systematic screening for the MET expression status using SP44 IHC showed discrepancy results according to the histological and the sample types. E-PS-15-004 EGFR assessment using next generation sequencing (NGS) as a reflex testing on surgically resected non-squamous non-small cell lung carcinoma (NS-NSCLC) C. Bontoux*, S. Goffinet, V. Hofman, F. Pezzuto, F. Calabrese, M. Ilié, P. Hofman *Laboratory of Clinical and Experimental Pathology, Hospital-Inte- grated Biobank (BB- 0033-00025), Pasteur Hospital, IRCAN Team 4, Inserm U1081, CNRS 7284, FHU OncoAge, Université Côte d’Azur, Nice, France Background & objectives: EGFR status assessment is mandatory in early-stage NS-NSCLC. Whether RT-PCR versus NGS should be used as reflex testing is still controversial. Co-occuring mutations, notably TP53 mutations, could have an impact on tumour behaviour and on adjuvant therapeutic strategies. Methods: EGFR mutations were assessed using DNA and RNA NGS (Oncomine Precision Assay genes panel) in 720 stage IA-IIIA sur- gically resected NS-NSCLC. PD-L1 expression was evaluated in all tumours. Results: EGFR mutations were detected in 11.5% tumours. A common non-compound EGFR mutation (L858R or del19) was observed in 75% of these latter cases. 55% of the global series has a co-occuring muta- tion, including a TP53 mutation, mostly in exons 7 and 8. EGFRmut/ TP53 mut tumours were significantly associated with higher PD-L1 expression compared to EGFRmut/TP53 wt tumours. Conclusion: Genomic alterations should be systematically evaluated using an NGS reflex testing in surgically resected NS-NSCLC, since future adjuvant therapeutic decision making may also take into account the presence of compound EGFR mutations as well as co-occuring mutations specially in TP53. E-PS-15-005 ALK protein expression and ALK mutations in neuroblastic tumours correlate with poor differentiation R. Bruinsma*, M. Fiocco, K. Langenberg, G. Tytgat, M. van Noesel, M. Wijnen, A. van der Steeg, R. de Krijger *Princess Máxima Center for paediatric oncology, The Netherlands Background & objectives: The anaplastic lymphoma kinase (ALK) gene has been identified as major oncogene for neuroblastic tumours (NBT). This study aimed to correlate the morphology of NBT, with genetic aberrations, immunohistochemical and mRNA expression of ALK. Methods: Diagnostic tumour samples were available from 182 patients. These patients were divided into two categories based on the international neuroblastoma pathology classification: undifferentiated and poorly differentiated neuroblastoma (n=134) versus differentiated neuroblastoma, ganglioneuroblastoma and ganglioneuroma (n=48 patients). ALK protein expression was scored following immunohisto- chemistry, while whole transcriptome sequencing yielded ALK mRNA expression levels. Results: ALK protein expression was categorized into three categories: negative (n=99), weak (n=30) and moderate/strong (n=37). The NBT were more often classified as undifferentiated or poorly differentiated in tumour samples that were ALK positive (negative versus weak OR 1.170, 95% CI (0.449-3.048)) (negative versus moderate/strong OR 2.279, 95% CI (0.803-6.471)). ALK amplification was only present in three NBT. ALK mutations (n=22) were more often seen in NBL that were undifferentiated or poorly differentiated (OR 2.056, 95% CI (0.576-7.341)). There was no correlation between the diagnosis category and mRNA expression level of ALK (OR 1.005, 95% CI (0.998-1.012)). Conclusion: Both ALK protein expression and ALK mutations are associated with poor differentiation degree in NBT, whereas mRNA expression levels are not. E-PS-15-006 Profiling spatial interactions of cancer-associated fibroblast sub- types in the wider tumour microenvironment of muscle invasive bladder cancer using multiplex immunofluorescence A. Burley*, T. Silveira, T. Lund, A. Melcher, N. James, A. Wilkins *Institute of Cancer Research, United Kingdom Background & objectives: Cancer-associated fibroblasts (CAFs) are a heterogenous population with reported pro-tumour, and some anti- tumour functions. In muscle invasive bladder cancer (MIBC), CAF- enrichment is associated with inferior survival outcomes following immunotherapy, surgery and chemotherapy. Yet, little is known about radiotherapy outcomes. Methods: Antibodies were optimised for immunohistochemistry and validated for single-plex immunofluorescence (IF) using the Opal sys- tem (Akoya). Staining order and antibody:opal pairings were consid- ered in the final multiplex design. Slides were stained using the Leica Bond autostainer, IF images were acquired using the Vectra Polaris (Akoya) and unmixed with inForm (Akoya). Results: The following antigens were selected for use in the multi- plex panel; aSMA (Abcam, 1A4), FAP (Abcam, EPR20021), PDG- FRa (Abcam, EPR22059-270), PDPN (Biolegend, D2-40), CD8 (Dako, C8/144B), panCK (Dako, AE1/AE3). The CAF markers selected reflect independent and co-expressing stromal populations. We found antigen stability was variable, and observed antigen deg- radation and enhancement, as such the panel and staining order was tailored accordingly. Quantification of the resulting images facilitates comparison with clini- cal data and helps to address our hypothesis that CAF enrichment in MIBC is associated with inferior survival outcomes and correlates with poor responses to radiotherapy. Conclusion: Transcriptomic/single cell studies of CAFs are limited due to difficulties distinguishing the origin of stromal signatures from bulk transcriptomic data, plus the spatial complexity of the tumour is lost. To overcome this, we have developed a novel CAF-specific mIF panel that offers an exciting and unique opportunity to explore the expression of multiple CAF markers in combination, their spatial arrangement, and their relationship with cytotoxic CD8+ T cells in the translational setting for MIBC patients treated with radiotherapy and beyond. E-PS-15-007 Real world evidence of RET fusion testing and prevalence in non- small cell lung cancer B. Cajiao Garcia*, V.D. de Jager, C. Kuijpers, A.J. van der Wekken, S.M. Willems, L.C. van Kempen, E. Schuuring *Department of pathology and medical biology, University of Gronin- gen, University Medical Center Groningen, The Netherlands Background & objectives: Molecular analysis is key to identify treat- ment options for non-small cell lung cancer (NSCLC) patients. Inhibi- tors for RET fusion-driven NSCLC have been approved. The objective of this study was to determine the national testing rate and incidence in the Netherlands. Methods: Clinical and pathology data from patients with stage IV non- squamous NSCLC diagnosed in 2017 and 2019 were collected from the Netherlands Cancer Registry (NCR) and linked to histopathology data collected in the Netherlands national registry of pathology reports (PALGA). RET fusion test rate, test type, timing of the test and test results were retrieved from these reports.