ECP 2023 Abstracts

S91 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 n=11 (13.9%) HPVI cases with gastric 45.4%, clear cell 27.3%, meso- nephric 18.2%, endometrioid 9.1%. 87.7% HPVA were positive for P16. HR-HPV RNA ISH was performed for 10 cases (HPVA 85.71% positive, HPVI 100% negative). Silva pattern of invasion(POI) for HPVA was Type A 14.7%; Type B 39.7%; Type C 45.6%. Nodal metastasis was observed in 21.9% HPVA, 28.6% HPVI cases. The mean follow-up time was 41.68 months (range 0.9–96). Recurrence free survival was 56.97 and 37.97 months for HPVA and HPVI cases respectively. Conclusion: IECC by morphology is highly reproducible. Sensitivity of P16 was 87.7% with PPV of 96.6%.HR-HPV RNA ISH remains a costlier approach and is highly dependent on tissue preservation and viral load. None of the cases with type A POI had nodal metastasis as compared to 45.5% with type B and 54.5% with type C POI. With respect to overall survival and recurrence free survival, HPVI cases (HR 1.84, 1.45,) as compared to the HPVA cases (HR 1.0, 1.0) (95% CI,p=0.3,0.4)respectively. Funding: Institutional intramural funding was received for this project. PS-10-024 Characterisation of uterine leiomyosarcomas: a single-centre ret- rospective study of 19 tumours D. Piñol Ballús*, A. Prat, S. Acosta, M. Miralles, M.C. Campos, E. Lerma, A. Gallardo *Hospital de la Santa Creu i Sant Pau, Barcelona, Spain Background & objectives: Uterine leiomyosarcomas (ULMS) are rare and aggressive tumours with a poor clinical outcome. The genetic complexity of ULMS is well-established. The objective of this study was to retrospectively analyse the molecular profile using surrogate immunohistochemical stains. Methods: We analysed the molecular profile of 19 patients with ULMS diagnosed at our institution between 2013 and 2023. Results: The study included 19 women aged 46-67 years with a recent diagnosis of ULMS. Thirteen patients presented with locally advanced metastatic disease at diagnosis, and seven patients died during follow-up. The tumours were located in the uterine corpus and ranged in size from 63-180 mm. All ULMSs showed smooth muscle differentiation and presented necrosis, severe pleomor- phism, and lymphovascular invasion. Tumour mitotic rate ranged from 7-70 mitosis/mm2. 12 tumours showed variable expression of hormone receptors. 4 tumours were focally positive for cytoker- atin markers. IHC analysis revealed mutations in TP53 (53%), ATRX (63%) and CDKN2A/p16 (89%). However, these molecu- lar alterations did not correlate with patient survival or mortality. Conclusion: TP53, ATRX, and CDKN2A/p16 are frequently mutated genes in ULMS. Hormone receptor expression and molecular altera- tions showed no correlation with patient survival. The frequent muta- tions in TP53, ATRX, and CDKN2A/p16 identified in our cohort sup- port their potential as biomarkers for ULMS diagnosis and prognosis. Further studies with larger sample sizes and longer follow-up periods are needed to confirm these findings and explore the clinical utility of these biomarkers. PS-10-025 HER2 testing in endometrial carcinoma, a summary of real world initial experience in a large tertiary cancer centre A. Plotkin*, E. Olkhov-Mitsel, S. Nofech-Mozes *Precision Diagnostics and Therapeutics Program, Sunnybrook Health Sciences Centre, Toronto, Department of Laboratory Medicine and Pathobiology, University of Toronto, Canada Background & objectives: Trastuzumab has been approved for treatment in HER2 positive endometrial serous carcinoma (ESC) based on results of randomized clinical trials. We audited our expe- rience in a tertiary care centre where testing is performed by clini- cian’s request. Methods: Endometrial carcinoma cases were tested by HER2 immunohistochemistry (IHC) using Ventana 4B5 antibody (Roche). Cases with equivocal IHC (score 2+) were further tested by dual- probe FISH assay (PathVysionHER2 DNA Probe kit). All cases were reported by one of two experienced HER2 FISH readers gynepathologists based on the practical recommendations proposed by ISGyP. Tumour characteristics were extracted from the pathol- ogy reports. Results: Over 18 months we tested 48 samples (from 47 patients); 47.9% were biopsies, 83.3% primary tumours, 52% serous and 48% non-serous endometrial cancer (EC) including 8.3% low grade endometrioid adenocarcinoma. Six cases were evaluated by two readers. HER2 was positive in 29.2% (35.7%- had IHC score 3+ and 64.3% showed HER2/neu gene amplification). The majority (78.6%) of positive cases showed heterogenous signal by either IHC or FISH. Among HER2 positive cases, 8 were ESC, 3 carcinosarco- mas, 2 (high grade) HG-NOS and 1 ambiguous. P53 was abnormal in 8 cases and unknown in 6. Conclusion: In our institution, about half of the requests for HER2 testing occurred in non-serous EC cases reflecting the notion that histologic subtyping of high grade EC is challenging as well as the limited management options for advanced EC. The frequent obser- vation of intratumoral heterogeneity raises the need to further study its potential role in trastuzumab resistance, benchmarking and pos- sible rational of testing antibody drug conjugates in endometrial carcinoma. PS-10-026 Clinicopathological features of 231 endocervical adenocarcinomas, including p16INK4a immunostaining results: a study at a tertiary cancer referral centre, India B. Rekhi*, A. Duggad, K. Deodhar, S. Menon, J. Ghosh, S. Gulia, T. Shylasree, A. Maheshwari *Department of Pathology Tata Memorial Hospital, Parel, India Background & objectives: There is no comprehensive study on clin- icopathological features of endocervical adenocarcinomas (ECAs), including HPV-related features and p16INK4a immunostaining from our country. This study was aimed at evaluating 231 ECAs, focusing on HPV-related morphological features and p16INK4a immunostaining with other parameters. Methods: Cases of ECA from Jan 2010-Dec 2015, including biop- sies and/ or resections were evaluated for HPV-associated morpho- logical features. p16INK4a(E6H4,Roche,USA) immunostaining was performed in 87(37.6%) tumours. Diffuse nuclear and cytoplasmic staining in >80% of tumour cells was considered as block-like/posi- tive result. Histopathologically, there were 174/231(75.3%) usual-type ECAs; 14(6.1%) gastric-type; 13(5.6%) villoglandular; 8(3.4%) endo- metrioid; 7(3%) mucinous/signet-ring cell and 15(6.4%) other types. Results: Age-range was 18-76 years (median=48). Stage- wise(n=142/231, 61.5%), most cases (67/142, 47.2%) were stage2, followed by stage1(45, 31.7%) and stage3(21,15%). There were 201/231(87%) tumours with HPV-associated morphological features. Most common HPV-associated was usual-type(174/201, 86.5%). The most common non-HPV-associated type was gastric-type(14/27, 51.8%). 63/87(72.4%) tested ECAs were p16INK4a-positive. 54/63(85.7%) tumours with HPV features were p16INK4a-positive.