ECP 2023 Abstracts

S56 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 repair gene mutation status to predict homologous recombination defi- ciency (HRD) in ovarian cancer (OvCa). As part of the ENGOT HRD initiative, we present updated clinical relevance results. Methods: Using SOPHiA DDM™Dx HRD Solution, DNA from a sub- cohort of 359 patients (pts) from the GINECO/ENGOT-Ov25 PAOLA-1 trial (NCT02477644) was re-analysed in a multicentre study. We com- pared the results to those previously obtained using Myriad myChoice CDx. We investigated differences in progression-free (PFS) and overall (OS) survival in the olaparib+bevacizumab and placebo+bevacizumab arms between HRD-positive and HRD-negative pts. Results: HRD status was determined in 98.9% of pts using SOPHiA DDM™ Dx HRD Solution. The overall concordance with Myriad myChoice CDx was 98.1% (95% confidence interval [CI], 96.0%- 99.1%) and highly reproducible across laboratories (r=0.987). In HRD-positive pts, the PFS and OS time were 55.7 months and 75.2 months respectively in the olaparib+bevacizumab arm versus 18.7 and 56.4 months respectively in the placebo+bevacizumab arm (hazard ratio [HR] PFS, 0.32; 95% CI, 0.22-0.45, p<0.001; HR OS, 0.49; 95% CI, 0.32-0.77, p=0.002). No significant difference in PFS or OS was observed between treatment arms in pts with HRD-negative test (HR PFS, 1.04; 95% CI, 0.71-1.52; p=0.8; HR OS, 1.19; 95% CI, 0.78- 1.80; p=0.4). Conclusion: The analytical performance and the potential clinical rel- evance results of SOPHiA DDM™ Dx HRD Solution from PAOLA-1 samples support the value of combining low-pass whole genome and targeted sequencing in a unique workflow for reliable and decentralized HRD testing and future patient stratification. MD-01-004 Optical genome mapping for comprehensive cytogenetic analysis of soft tissue and bone tumours J. Baelen*, I. Vanden Bempt, P. Schöffski, R. Sciot, B. Dewaele *KU Leuven, Belgium Background & objectives: In soft tissue and bone tumours (ST&BT), identification of structural variants (SV) and copy number alterations (CNA) is challenging but essential for accurate diagnosis. We intro- duce optical genome mapping (OGM) for comprehensive SV and CNA detection in diagnostic ST&BT samples. Methods: Ultra-high molecular weight DNA was extracted from a series of 55 snap-frozen diagnostic ST&BT samples, diagnosed between 2015 and 2022 at the University Hospitals Leuven. DNA was labelled and optically imaged; data was analysed using the rare variant analysis/de novo assembly pipeline (Bionano Genomics). Results were compared to karyotyping, fluorescent in situ hybridization (FISH) and/ or RNA sequencing. Results: In total, 39 samples comprising 20 ST&BT subtypes were successfully analysed by OGM (39/55, 71%). Highest success rates were obtained in undifferentiated small round cell sarcomas (USRCS) of bone and soft tissue (6/6, 100%). OGM identified diagnostic SV/ CNA in 36 out of 39 samples (92% concordance to standard-of-care). In those 39 samples, 3 out of 20 unique SV/CNA were not detected by OGM: CIC::DUX4, STAT6::NAB2 and heterogeneous MDM2 ampli- fication. Of interest, OGM identified additional SV/CNA, including the recently described EWSR1::COLCA2 fusion in an USRCS and a novel TGFBR3::CLPTM1L translocation in a myxoinflammatory fibroblastic sarcoma. No false positive diagnostic SV/CNA were found by OGM. Reproducibility was demonstrated in 3 duplicate analyses. Conclusion: OGM was successful in a variety of ST&BT subtypes with highest success rates obtained in USRCS of soft tissue and bone (100%). OGM identified diagnostic SV/CNA in 92% of cases, compared to combined state-of-the-art diagnostic testing. Impor- tantly, OGM allowed identification of additional SV and CNA that remained undetected by current cytogenetic tools. We conclude that OGM has the potential to improve diagnostic cytogenetic testing for ST&BT, allowing more comprehensive and highly sensitive and specific detection of SV and CNA. Funding: JB receives funding via “Kom Op Tegen Kanker/Fonds Wetenschappelijk Onderzoek IVB is recipient of a post-doctoral man- date from the Klinische onderzoeks- en opleidingsraad (KOOR) of the University Hospitals Leuven Poster Sessions PS-01 | Poster Session Breast Pathology PS-01-001 Inter-laboratory variability of HER2-low analysis using artificial intelligence N. ’t Hart*, M. Eenkhoorn, H. Høeg, D. Dabbs *Isala, The Netherlands Background & objectives: Treatment of HER2-positive breast car- cinoma is emerging for HER2-low expressing tumours. In this study, immunohistochemical detection of HER2-low is tested for inter-and intra-laboratory reproducibility in The Netherlands. Methods: To define reproducibility of HER2-low, three blanc slides with a dynamic range cell line (HistoCyte, Newcastle,UK) were send to 42 labs. Participants were asked to stain slides in three consecutive days. After staining, slides were scanned and analysed using AI-software (Qual- itopix, Visiopharm, Hoersholm,DK). Membrane staining intensity was measured for all cells and a score (0-100) was determined for each core. Results: Four antibodies were used by 32 laboratories: 59.4% clone 4B5, 9.4% Herceptest (DG44), 15.6% SP3 and 15.6% C-erbB-2. Sum- mary statistics are calculated across different antibodies per core. The middle core of the cell line showed the most variation and is shown here as a striking example. Clone 4B5 scored 44.07+/-9.45% (mean+/-SD) and DG44 scored 72.57+/-3.99%. Both 4B5 and DG44 are monoclonal antibodies of Ready To Use kits. Monoclonal SP3 is used at dilutions ranging from 1:200 to 1:1000, polyclonal C-erbB-2 dilutions varied between 1:200 and 1:500. The negative core showed a positive result for both SP3 and C-erbB-2. The middle core scored 42.83+/-11.01% for SP3 and 71.20+/-20.11% for C-erbB-2. Conclusion: Four HER2 antibodies were used in Dutch laboratories. 4B5 and DG44 showed consistent HER2 results. C-erbB-2 and SP3, however, demonstrated HER2-positive results in negative controls. Furthermore, C-erbB-2 and SP3 were used with different antibody concentrations show- ing inconsistent HER2-expression. Overall, HER2 antibodies need to be re-validated and the use of a standardized reference material (e.g. cell lines) with AI is a promising method to determine HER2-low for clinical use. Funding: AstraZeneca Nederland PS-01-002 Androgen receptor mRNA is associated with better survival outcomes in triple negative breast cancer S.S. Ahmed*, D.Y. Lee, C.H.C. Ong, B. Lee, J.P.S. Yeong, J. Iqbal *Singapore General Hospital, Department of Anatomical Pathology, Singapore Background & objectives: This study aims to evaluate the gene expression of AR in triple negative breast cancers (TNBC), analyse the relationship between AR transcriptional expression with clinico- pathological parameters and survival outcomes and to spot a panel of AR-correlated hub-genes with prognostic value. Methods: Tissue microarrays (TMA) were constructed from formalin fixed paraffin (FFPE) embedded tissue of 389 TNBCs diagnosed at Singapore General Hospital. NanoString mRNA extraction and Digital mRNA quan- tification using NanoString assay were performed on TMA and analysed.