ECP 2023 Abstracts

S61 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 Conclusion: We identified post-NACT rLVI as a strong factor predictive of poor DFS in retrospective series of 655 BC patient treated by NACT and surgery and evaluated by RCB prognostic scoring system. The effect was lost on multivariate analysis, while RCB status remained significant. Residual LVI should be systematically reported in post-NACT pathology reports and could serve as indicator of poor survival in cases where RCB score cannot be calculated with certainty (e.g., in false negative sentinel lymph node biopsy). PS-01-017 Lack of deletion of 1p36 in primary adenoid cystic carcinoma of the breast G. Gasljevic*, B. Grcar-Kuzmanov, S. Borstnar, J.A. Contreras Bandres *Institute of Oncology Ljubljana, Slovenia Background & objectives: Breast adenoid cystic carcinoma (B-AdCC) is a rare salivary gland-type tumour. In salivary gland AdCC, deletion 1p36 associates with solid histology and aggressive course. The aim of the study was to investigate its existence and prognostic value in 21 B-AdCCs. Methods: Twenty-one B-AdCC diagnosed from 1985-2022. were included in the study. Tissue microarrays were constructed by sampling cores of 2-mm diameter from area of conventional and/or solid basaloid type as well as from high grade transformation. For the detection of 1p36 locus deletion by FISH, ZytoLight® SPEC 1p36/1q25 Dual Color Probe (ZytoVision GmbH) was used. Results: Seven tumours (33.3%) were pure conventional B-AdCC, 4 (19%) were pure basaloid B-AdCC while 9 (42.8%) had between 10-90% of solid basaloid component. One (4.7%) was AdCC with high grade transformation. All 21 cases were analysable by FISH. Follow-up was available for all patients. All the cases, including 2 patients who died of metastatic disease as well as the patient with B-AdCC with high grade transformation, proved to be negative for 1p36 deletion. Conclusion: Our results show that the deletion of 1p36 is not a feature of B-AdCC and cannot be used as a prognostic marker. Further studies on larger series are needed to confirm this assumption. PS-01-019 Hypoxia and immune evasion in young women with breast cancer: a population-based study R. Humlevik*, A. Svanøe, G. Knutsvik, A. Sæle, C. Askeland, L. Ingebriktsen, U. Hugaas, A. Kvamme, K. Krüger, B. Davidsen, T. Aas, I. Stefansson, E. Hoivik, L. Akslen, E. Wik *University of Bergen, Norway Background & objectives: Young women, below 40 years, present higher frequency of aggressive tumour features and poor prognosis. We aimed to investigate the relationship between age and breast cancer related biomarkers and biology, with emphasis on hypoxia and immune evasion. Methods: Clinico-pathologic variables was obtained from of a population-based cohort of women aged under 50 (n=355) and com- pared to a previously described cohort of breast cancer patients aged 50-69 (n=543). The tumour infiltrating lymphocyte (TIL) mark- ers CD45 and CD8 were stained by immunohistochemistry. Data from the METABRIC cohorts was applied for analyses of stemness, immune, and hypoxia-related gene expression signatures. Results: Young patients presented with aggressive tumour features and shorter survival. Ki67 showed a weaker prognostic value within the young group. Young age was associated with gene-scores reflect- ing increased hypoxia. High levels of CD45+ and CD8+ TILs were associated with the triple negative and basal-like subtypes, and there was a trend towards higher levels of CD45+ TILs in young women. Age below 40 was significantly associated with transcriptional patterns of stemness and the basal-like marker CK5/6. Young women showed significantly higher expression of genes contributing to an immune evasive environment, including CTLA4 and PD1, and lower expression of B7-H4. High expression of CTLA4 and PD1 mRNA was associated with poor survival. Conclusion: Our population-based study confirms previous findings of a more aggressive breast cancer phenotype in patients below 40 years. We demonstrate increased expression of markers tumour cell prolifera- tion, stemness, hypoxia, and an immune evasive environment in young breast cancer patients. Hence, tumours of young breast cancer patients may have a unique biology that may open for new clinical opportunities stratifying treatment by age. The work was supported by the University of Bergen and the Research Council of Norway through its Center of Excellence funding scheme (project number 223250), and through the Helse Vest Research Fund (F-12143 and F-12596). PS-01-020 Assessment of PD-L1 expression in triple-negative breast carcinoma: the first north African case series M. Khmou* *National Institute of Oncology, Morocco Background & objectives: TNBC are not sensitive to endocrine ther- apy or HER2 treatment. Recent advances have led to the development of immune-checkpoint-inhibitors and have shown survival improve- ments. The aim of this study is to report PD-L1 expression in TNBC among the Moroccan population. Methods: We investigated PD-L1 expression by immunohistochem- istry in TNBC, without neoadjuvant chemoradiotherapy, diagnosed at the department of pathology at the National Institute of Oncology in Rabat, from January 1st, 2021, to December 1st, 2021. Fifty-four biopsy samples with sufficient tumour tissue were selected. Antibody clone 22C3 was used and PD-L1 expression was evaluated using the Combined positive score (CPS). Results: The study included 54 cases of TNBC. 15 out of 54 cases (27.8%) had PD-L1 CPS score ≥10. The mean age of our patients was 53 years, with extremes ranging from 32 to 81 years. The most common his- tological type was invasive carcinoma of no special type (90.7%). PD-L1 expression was significantly correlated with high tumour-infiltrating lymphocytes (TILs). There was no statistically significant relationship between PD-L1 expression and other clinicopathological parameters. Conclusion: Our study showed that 27.8% of our patients had PD-L1 CPS score ≥10, and higher TILs were significantly correlated with the PD-L1 expression CPS score. Thus, these findings may be useful for setting new therapeutic guidelines in our country, aiming for a better outcome. Our study is the first to report PD-L1 expression in TNBC among the Moroc- can population and has several main limitations, as it is a retrospective analysis with a small-sized sample which may lead to selection bias. PS-01-021 A Canadian experience in proficiency testing for HER2-low breast cancers Z. Kos*, J. Garratt, J. Won, B. Sheffield, B. Gilks *BC Cancer Vancouver Centre, Canada Background & objectives: Novel anti-HER2 compounds are trans- forming the traditional dichotomy of HER2 status in breast can- cer, commonly defined by immunostaining and in situ hybridiza- tion assays. We share findings from a proficiency testing scheme for HER2-low breast cancers in which 35 laboratories participated. Methods: The CPQA-AQCP provided an unstained section of a 43-core breast carcinoma tissue microarray to participating laboratories for HER2 immunostaining as per routine testing methodologies. Results were