ECP 2022 Abstract Book

Virchows Archiv (2022) 481 (Suppl 1):S1–S364 13 insufficiently specific to reliably predict metastatic behaviour. This is, however, a first step towards the development of a predictive algorithm on which therapeutic strategies can be based. We are cur- rently investigating additional parameters such as tumour microen- vironment as well as additional histological and clinical parameters to improve the specificity of our predictive model. OFP-06-014 Expression of phagocytosis markers and phagocytosis inhibi- tors in Usual Interstitial Pneumonia (UIP) M. Neururer*, L. Brcic, S. Eidenhammer, H. Popper *Medizinische Universität Graz, Austria Background & objectives: Fibrosis in UIP is facilitated by senescence cells, which secrete inflammatory cytokines. Phagocytosis counteracts the inflammation by removing cellular debris. We want to identify cells expressing phagocytosis- associated molecules and cells protecting themselves by expressing CD47 within the peripheral lung. Methods: We performed immunohistochemistry on 44 cases of UIP with different aetiology using antibodies against LAMP1, Rab7, TRAP (all phagocytosis-associated), and CD47 (phagocytosis-protecting). Results: Phagocytosis-associated molecules were expressed in all macrophages, but also by a considerable proportion of regenerating cells within the remodelled areas. Myofibroblasts, endothelia, and bronchial/bronchiolar epithelial cells were all negative. Expression of LAMP1 and Rab7 were sometimes focally seen in type II pneumocytes within normally structured lung. CD47 was expressed by macrophages, but also by few regenerating epithelial cells within the remodelled peripheral lung, much less compared to the expression of phagocytosis markers. As we suspected these to be senescent cells, we performed double immunohistochemical staining for p16 (senescence marker) and CD47. Conclusion: Our results indicate that senescence cells have prob- ably activated a mechanism, protecting them from being attacked and phagocytosed by leukocytes. Thus, they maintain inflammation and proliferation of myofibroblasts. OFP-06-015 Large-scale human tissue analysis identifies Uroplakin 3B as a useful diagnostic marker for mesothelioma and normal meso- thelial cells V. Reiswich, D. Atug, C. Fraune, R. Uhlig, V. Chirico, C. Völkel, T.S. Clauditz, F. Büscheck, A. Marx, F. Jacobsen* *University Medical Center Hamburg, Germany Background & objectives: Uroplakin 3B (Upk3b) stabilizes the urothelial cell layer lining the bladder. Based on RNA expression studies Upk3b is expressed in a only limited number of normal tis- sues and tumour entities. This study assessed the diagnostic utility of Upk3b immunohistochemistry. Methods: A set of tissue microarrays containing 8071 sam- ples from 125 different tumour types and subtypes and 608 samples of 76 different normal tissue types was analysed by immunohistochemistry. Results: Normal cell expression of Upk3b was largely limited to mesothelial cells, umbrella cells of the urothelium, and amnion cells. Upk3b was detectable in 13 (10,4%) of 125 tumour entities. The rate of Upk3b positivity was highest in malignant epitheloid mesotheliomas (81,5%), followed by various categories of urothe- lial tumours (14,6-45,7%) including Brenner tumours of the ovary (10,8%), four further subtypes of ovarian cancers (1,1-10,4%) and adenocarcinoma of the ampulla of Vater (2,7%). Within urothelial tumours, Upk3b positivity decreased from 45,7% in pTaG2 (low grade) to 34,2% in pTaG3 (high grade), and 14,6% in pT2-4 cancers (p<0,0001). Within pT2-4 cancers, Upk3b staining was unrelated to pT, pN, and patient prognosis. Conclusion: Upk3b immunohistochemistry is a useful diagnos- tic tool for the distinction of mesotheliomas from other thoracic tumours and the visualization of normal mesothelial and umbrella cells. OFP-06-016 The relationship of VSIR(VISTA) and PD-L1 expressions with histologicalsubtypes in mesothelioma M. Dicleli* *Dicle University, Faculty of Medicine, Department of Medical Pathology, Turkey Background & objectives: Mesothelioma is a tumour with low response to treatment and poor prognosis. This has led to the search for new treatment methods such as antibodies that block immunocontrol points. We evaluated the immune checkpoint markers PD-L1 and VISTA in mesotheliomas. Methods: VISTA and PD-L1 expression analysed in 45 epithelioid,10 sarcomatoid, 9 biphasic mesotheliomas 3 well- differentiated mesothelial tumours (WDPMT) and 2 atypical mesothelial proliferation cases (AMP). Positive staining for VISTA in tumour cells was defined as the presence of any cytoplasmic and/or membranous staining, and for PD-L1, the presence of any membranous staining. Results: Positive VISTA staining was seen %91 of cases, more frequently in epithelioid (%98) and biphasic (89%) compared to sarcomatoid (60%) mesotheliomas. Benign mesothelium, WDPMT, AMP, testicular and peritoneal mesotheliomas were all positive with VISTA. PD-L1 was expressed more frequently in sarcomatoid (80%) mesotheliomas compared to epithelioid (29%) and biphasic (33%) mesotheliomas. All PD-L1 positive cases were pleural mesothelioma except 2 epithelioid peritoneal meso- thelioma. While 1/23 low-grade and 10/17 high-grade pleural epithelioid mesotheliomas were positive with PD-L1. A signifi- cant correlation was found between VISTA(p=0.00) expression with epithelioid mesotheliomas, while PD-L1 expression with sarcomatoid (p=0.01) and high-grade epithelioid mesotheliomas (p=0.00). An inverse negative relationship between VISTA and PD-L1 scores was observed. Conclusion: VISTA expression was observed more frequently in sarcomatoid mesotheliomas compared to epithelioid meso- theliomas, while PD-L1 expression was mostly observed in sarcomatoid mesothelioma. It is known in the literature that PD-L1 expression is associated with a bad prognosis and VISTA expression is associated with a good prognosis. We also observed higher PD-L1 expression in high-grade epithelioid mesothelioma than in low-grade. We wanted to emphasize the importance of the expression of immuc check point inhibitors in mesothelioma subtypes in target-directed drug selection. OFP-07 | Oral Free Paper Session Dermatopathology OFP-07-001 Mutations detected by next generation sequencing in primary and metastatic melanoma samples and correlation with clin- ico-histopathological parameters J.B.S. Liu, K. Zwaenepoel, K. De Winne, A. Pouliakis, P. Pau- wels, V. Siozopoulou* *Department of Pathology, Antwerp University Hospital, Ede- gem, Belgium S27