ECP 2023 Abstracts

S50 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 p-value=0.06). When using cluster interactions as features for the Cox regression, we obtained a mean c-index of 0.615 (0.567, 0.662) with statis- tically significant difference between low- and high-risk groups (HR=1.54, p-value=0.03). Combining PD-L1 expression with cluster-based features increased the mean c-index to 0.666 (0.654, 0.678) with a sharper difference between low- and high-risk groups (HR=2.06, p-value<0.001). Conclusion: Using whole-slide images only, we were able to devise a new set of features to predict survival for patients receiving ICI treat- ment consequent to lung cancer. Our method combines a deep learn- ing-based clustering approach with a Cox PH regression to output the survival probability after treatment. We show that the newly created features had a predictive power comparable to PD-L1 expression. The combination of the two showed even more promising results to distin- guish low- and high-risk groups. OFP-13-004 N-glycomic signature of microsatellite unstable colorectal cancer I. Ukkola*, P. Nummela, A. Heiskanen, M. Holm, S. Zafar, M. Kero, C. Haglund, T. Satomaa, S. Kytölä, A. Ristimäki *Department of Pathology - HUSLAB, Helsinki University Hospi- tal and University of Helsinki, Finland, Applied Tumour Genomics Research Program – Faculty of Medicine, University of Helsinki, Finland Background & objectives: Approximately 15% of colorectal cancers (CRCs) display microsatellite instability (MSI) and show major dif- ferences in outcome and therapeutic responses as compared to micro- satellite stable (MSS) CRCs. The molecular CRC subtypes have been largely ignored in previous glycomics studies. Methods: We compared the N-glycan profiles of stage II and IV MSI CRCs, further subdivided into BRAFV600E mutated (mt) or wild-type (wt) subgroups (n=10 in each group), with each other and with non-neo- plastic colon control samples using MALDI-TOF mass spectrometry. In addition, the N-glycan profiles of the stage II BRAFwt MSI tumours were compared to corresponding MSS tumours analysed previously (n=9). Results: In line with previous CRC reports, MSI CRC tumours displayed higher relative abundance of neutral pauci-mannose but in contrast lower abundance of high-mannose N-glycans than the control tissues. Between stage II MSI and MSS CRCs, especially the acidic N-glycan profiles markedly differed, MSI tumours showing lower relative abundances of large, sulfated, terminal N-acetylhexosamine (HexNAc) containing, and fucosylated N-glycans. Striking differences were also seen in the acidic N-glycans of MSI subgroups. Most interestingly, the large, sulfated, and terminal HexNAc containing N-glycans were more abundant in BRAF- mut than BRAFwt stage IV MSI tumours, whereas in stage II they were less abundant in BRAFmut than BRAFwt tumours. Conclusion: In conclusion, the neutral and acidic N-glycan profiles of stage II MSI CRC tumours differ from the corresponding MSS tumours. Most importantly, the acidic N-glycan profiles show a clear dependency on tumour stage and BRAF mutation status in MSI CRC. Our results show that the molecular subgroups of CRC have unique glycan profiles, which may partly explain their tumorigenic and immunogenic proper- ties. These glycosylation alterations could thus predict the progression and therapy responses of MSI CRCs after further validation. Funding: Cancer Foundation Finland, Finska Läkaresällskapet, Hel- sinki University Central Hospital Research Funds, Medicinska Under- stödsföreningen Liv & Hälsa, Orion Research Foundation, Sigrid Jusé- lius Foundation, and University of Helsinki. OFP-13-005 Detection of tumour DNA in bronchoscopic fluids in confirmed or suspected lung cancer: a proof-of-concept study N. Piton, G. Arhant, S. Lachkar, P. Thiebaut*, F. Marguet, A. Lamy, L. Thiberville, M. Salaün, F. Guisier, J. Sabourin *Rouen University Hospital, France Background & objectives: Genotyping of circulating tumour DNA is a useful tool for characterization of lung cancer, but with low sensitivity. Our aim was to detect tumour DNA in the supernatant of guide sheath flush fluids collected during bronchoscopy. Methods: Total DNA was extracted and genotyped using high-throughput sequencing or the COBAS®EGFRMutation Test. Thirty-three paired sam- ples (supernatant of guide sheath flush + plasma) from 24 newly diagnosed patients and 9 progressive non-small cell lung cancer patients were analysed. Results: Guide sheath flush-based genotyping yielded a mutation detection rate of 61.8% (17/24 EGFR, 1/2 ERBB2, 1/1 KRAS, 1/1 MAP2K, 1/4 MET, and 0/1 STK11), compared to 33% in plasma-based genotyping (p = 0.0151). Conclusion: The detection of tumour DNA in the supernatant of guide sheath flush fluid collected during bronchoscopy represents a feasible and more sensitive alternative to circulating tumour DNA genotyping in non-small cell lung cancer. This work was mainly funded by Boehringer Ingelheim® (“Bourse Régionale Profil Onco 2015” awarded to Nicolas Piton). OFP-13-006 Molecular characterization of metastatic breast carcinomas by NGS on circulating tumour DNA P. Santiago Díaz*, S. Clavé Safont, R. Longarón Rozalen, A. Escobar Tejeda, G. Piquer Velasco, I. Vázquez de las Heras, L. Comerma Blesa, B. Lloveras Rubio, B. Bellosillo Paricio *Hospital del Mar, Barcelona, Spain Background & objectives: Cell-free DNA (cfDNA) analysis is use- ful to identify actionable alterations, monitor treatment response and evaluate clonal heterogeneity. The aim of this study was to evaluate the clinical utility of cfDNA analysis in breast cancer patients by next- generation sequencing (NGS). Methods: 26 cases of metastatic breast cancer were prospectively selected and analysed using Oncomine Breast cfDNA Research Assay v2 NGS panel (ThermoFisher) on cfDNA (24 blood samples, 1 pleural fluid and 1 cerebrospinal fluid). Cases with no alterations detected on cfDNA were studied performing NGS on DNA from FFPE tumour tissue. cfDNA con- centration (ng/ml) and limit of detection (LoD%) were annotated. Results: Molecular alterations were detected in 18 out of 26 cases. 16 cases harboured 1-2 alterations, with 6 being the maximum number detected in a single case. PIK3CA was mutated in 13 of 18 cases, fol- lowed by TP53 (8 cases, 6 showed coexistence with PIK3CA). Other alterations were found on ESR1, SF3B1 and FGFR1. No cfDNA abnor- malities were observed in 8 cases (31%). FFPE tumour tissue charac- terization showed gene mutations (PIK3CA, ERBB2 and FGFR1) in 4 of them, and no alterations in the other 4 cases. Cases with detectable alterations showed higher cfDNA concentration (73.1 vs. 63 ng/ml), and higher sensitivity (LoD%: 0.3% vs. 0.9%). Conclusion: The application of NGS panels on cfDNA allowed the molec- ular characterization of patients with metastatic breast cancer in combina- tion with the study of tumour tissue samples in 22 out of 26 (85%) cases. Despite the limitation of the low number of cases in our series, this work suggests that the detection of gene mutations in cfDNA correlates with cfDNA concentration. OFP-13-007 Lineage-specific molecular differences in the development of brain metastasis from lung adenocarcinoma and breast cancer J. Kros*, S. Najjary, w. de Koning, C. van Eijck, D. Mustafa *Dept. of Pathology, Erasmus Medical Center, The Netherlands Background & objectives: In order to find drugs preventing the for- mation of cerebral metastases, or interfere with outgrowth in brain, we aimed to identify the involvement of molecules or pathways in tumours of different lineages.