ECP 2023 Abstracts

S25 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 (9%,N=3). PA harbored in 12 cases (30%) CTNNB1::PLAG1 fusion, and ZBTB47-AS1::PLAG1 in 6 cases (N=15%). Others fusion partners of PLAG1 included CHCHD7, NCALD, ACTA2, LIFR, BOC, CARMN, CRISPLD1, EIF4G2, FBXO32, GEM, OSR1, TGFBR3, and in one case TRPS1. Both CMT and PA shared same histological features. Statistically, gene fusion involving TRPS1 was more frequent in CMT(p<0.001). Conclusion: This study highlights that although CMT and PA share almost the same morphological features and PLAG1 gene fusions, fusion partners are different between the 2 tumour groups. CMT are mainly characterized by TRPS1::PLAG1 gene fusion, while PA exhibit a broad spectrum of PLAG1 gene fusion part- ners, with exceptional TRPS1 usage. This study provides the first detailed comparison between CMT and PA, emphasizing on their molecular distinctiveness and its potential diagnostic utility in clinical practice to determine the tumour origin. OFP-06-008 MicroRNA expression in oropharyngeal squamous cell carcinoma – searching for novel prognostic biomarkers in a clinico-patholog- ical and molecular genetic study of 73 patients J. Laco*, H. Parova, N. Birknerova, I. Baranova, H. Vosmikova, B. Gajdosova, M. Hodek, M. Vosmik, M. Chmelarova, P. Celakovsky, A. Ryska *Faculty of Medicine Hradec Kralove Department of Pathology, Czech Republic Background & objectives: MicroRNAs (miRNAs) have been rec- ognized as key molecules in cancer development and progression. The aim of our study was to determine relative miRNA expression in metastasizing oropharyngeal squamous cell carcinoma (OPSCC) and to find correlation with clinico-pathological characteristics. Methods: A total of 190 samples were analysed in the study (73 primary tumours with 73 corresponding lymph node metastases, and 44 control samples). In every patient, classical clinicopatho- logical parameters were recorded. For miRNA expression, both miRNA microarray analysis and small RNA sequencing were per- formed to select significantly dysregulated miRNAs, which relative expression was subsequently verified using qPCR analysis. Results: The study sample comprised 55 males and 18 females, aged 41–80 years (median 58 years). A total of 81% of tumours were HPV-DNA/p16-positive. During the follow-up period (range 3–200 months; median 97 months), 18% of tumours recurred and 14% of patients died due to the tumour. We observed significant upregulation of both miR-206 and miR-3656 and downregulation of miR-150-5p in primary tumours compared to controls (p < 0.05). The trend for more prominent downregulation of miR-150-5p in HPV-negative OPSCC was found (p = 0.07). Kaplan-Meier sur- vival curve showed that patients with lower expression of miR- 150-5p had impaired overall survival compared to patients with higher expression (p = 0.01). Conclusion: In summary, both significant dysregulation of selected miRNAs in tumour samples versus controls and correla- tion with recorded clinico-pathological parameters was observed in our OPSCC study sample. Notably, miR-150-5p might become a novel prognostic marker in these malignancies. In general, our promising results unravel novel potential biomarkers which, if confirmed by further studies, could be used as prognostic markers in the sense of tailored therapy and treatment individualization of patients with OPSCC. Funding: Supported by the project BBMRI-CZ LM2018125, by the European Regional Development Fund-Project BBMRI-CZ.: Biobank network – a versatile platform for the research of the etiopathogenesis of diseases, No: EF16_013/0001674, and by the Cooperatio Program of Charles University (research area DIAG). OFP-06-009 Sinonasal DEK/AFF2 carcinoma: 11 additional cases with new histological features A. Trinquet*, M. Laé, M. Hourseau, V. Costes-Martineau *CHU Gui de Chauliac, France Background & objectives: Sinonasal carcinoma with DEK/AFF2 rearrangement is an entity of recent discovery with few described cases. We described the morphological and immunophenotypic characteris- tics of eleven additional cases in order to better recognize them and to investigate their prognosis. Methods: We studied a cohort of 11 patients diagnosed with DEK/ AFF2 carcinoma, within the framework of RefCor network. Epidemiological data (gender, age), tumour-, treatment-related and prognostic data (location, extension, treatment, relapse, death) were retrospectively analysed. Morphological and immunophenotypic features were reviewed by two pathologists. We then combined these data with data of the 29 previously published cases. Results: In our cohort, these tumours displayed several recurrent aspects, the most constant ones being the presence of a mixed exo- endophytic pattern, cytological monotony and the most striking aspect being the presence of an abundant inflammatory infiltrate rich in neu- trophils. We also described one case with an unusual biphasic pattern. All tumours expressed P40. CK7, PDL1 and P53 expression were vari- able, and P16 was not overexpressed. On the prognostic level, when combined to other published cases, 57% of patients showed local recurrence or tumour progression, 24%, lymph node involvement, 21% distant metastatic involvement and 14% disease-related death. Conclusion: Carcinomas with DEK/AFF2 rearrangement show some particular histological features. Few cases have been described so far and the follow-up time of patients is still too short to evaluate the prognostic impact or the theranostic interest of this molecular anomaly. Thus, a research of this translocation on a larger number of sinonasal papillary P16 negative tumours would be desirable to clarify these aspects and could also be a diagnostic aid because malignancy is some- times difficult to assert in these cases. OFP-06-010 Independent validation of somatostatin receptor 2 as a sensitive and specific biomarker for Epstein-Barr virus status in sinonasal/ nasopharyngeal squamous cell carcinoma K. Viswanathan*, C. Marcus, S. Muzahir, S. Steward-Tharp *Emory University Hospital Midtown, USA Background & objectives: Epstein-Barr virus (EBV), a known nasopharyngeal carcinoma (NPC) driver, promotes somatostatin receptor 2 (SSTR2) expression via NF-KB. SSTR2 is detectable by immunohistochemistry, however, validation data on whether SSTR2 immunohistochemistry can distinguish EBVNPC from non-EBV squamous cell carcinoma (SCC) is limited. Methods: SSTR2 immunohistochemistry was performed on our cohort of EBVNPC (n=15), HPV-positive sinonasal SCC (n=7, HPVSCC), and virus-negative sinonasal SCC (n=8, VNSCC). Slides were reviewed by two board-certified pathologists and an H-score was cal- culated using the intensity and extent of tumour staining. Cases were also scored as positive or negative. Clinical outcomes and demographic information were obtained from the medical charts. Results: Using a positive/negative system, 93.3% EBVNPC (n=14/15), 14% HPVSCC (n=1/7), and 25% VNSCC (n=2/8) demonstrated mul- tifocal to diffuse strong SSTR2 expression. The sensitivity, specificity, negative predictive value, and positive predictive values for SSTR2 IHC were 93.3%, 80%, 92.3%, and 82.4%, respectively. The median