ECP 2023 Abstracts

S78 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 Conclusion: Pre-analytical effects in IHC can be minimized with stand- ardization of specimen handling leading to enhanced specimen quality and antigen preservation. FFPE tissues prepared with various ischemic times ranging from 0-24 hours and fixation times ranging from 6-72 hours demonstrated negligible variability in intensity between condi- tions and was well within the expectations of IHC staining. PS-07-008 Prostein expression in human tumours: a tissue microarray study on 19,202 tumours F. Viehweger*, M. Lennartz, N. Blessin, C. Hube-Magg, D. Dum, A. Menz, R. Uhlig, E. Burandt, G. Sauter, R. Simon, M. Kluth, S. Steurer, T.S. Clauditz, C. Bernreuther, S. Kind *Institute of Pathology, University Medical Center Hamburg-Eppendorf, Germany Background & objectives: Prostein (P501S), also termed solute car- rier family 45 member 3 (SLC45A3) is an androgen regulated protein which is preferentially expressed in prostate epithelial cells. Because of its frequent expression in prostate cancer, prostein was suggested a diagnostic prostate cancer marker. Methods: In order to comprehensively assess the diagnostic util- ity of prostein immunohistochemistry, a tissue microarray containing 19,202 samples from 152 different tumour types and subtypes as well as 608 samples of 76 different normal tissue types was analysed by immunohistochemistry. Results: Prostein immunostaining was typically cytoplasmic, granular and perinuclear and predominated in prostate cancer. Prostein positiv- ity was seen in 96.7% of 419 prostate cancers including 78.3% with a strong staining. In 12,233 extra-prostatic tumours, prostein positivity was observed in 9.8% of cases but only 0.4% had a strong staining. Extra-prostatic prostein positive tumours were 50 different tumour cat- egories, 12 of which included at least one strongly positive case. Extra- prostatic tumours with highest rates of prostein positivity included salivary gland tumours (7.6%-44.4%), neuroendocrine neoplasms (15.8%-44.4%), adenocarcinomas of the gastrointestinal tract (7.3%- 14.8%), biliopancreatic adenocarcinomas (3.6%-38.7%), hepatocellular carcinomas (8.1%), and adenocarcinomas of other organs (up to 21%). Conclusion: In summary, our data provide a comprehensive overview on prostein expression in human cancers. Prostein is a highly sensitive prostate cancer marker occurring in >96% of prostate cancers. Because prostein can also be expressed in various other tumour entities, label- ling of a tumour mass as a prostate cancer should not be based on prostein positivity alone. PS-08 | Poster Session Dermatopathology PS-08-001 PRAME expression and its relationship between clinicopathologi- cal parameters and immunological markers in melanoma: an in- silico analysis Y. Cakir*, Z. Sağnak Yılmaz, B. Lebe *Dokuz Eylül University, The Institute of Health Sciences, Department of Molecular Pathology, Turkey Background & objectives: PRAME is a cancer-testis antigene which showed differential expression in cancers compared to normal tissue. However, its role in immune infiltration and immunotherapy is contro- versial. We investigated the association between PRAME expression and clinicopathological/immunological characteristics in melanoma with bioinformatic tools. Methods: The cBio Cancer Genomics Portal (cBioPortal), The Uni- versity of Alabama at Birmingham Cancer data analysis Portal (UAL- CAN), Tumour Immune Estimation Resource (TIMER2.0), Gene Expression Profiling Interactive Analysis (GEPIA2), the Tumour– Immune System Interactions and Drug Bank (TISIDB) databases were used to explore the effect of PRAME expression on clinicopathologic features, immune infiltration, survival, the correlation with immune checkpoint genes expression. Results: TCGA and metastatic melanoma (DFCI, UCLA) datasets were investigated in UALCAN and cBioPortal databases. The higher PRAME expression levels were detected in cases with higher T/N stage, meta- static and p53 non-mutant cases (p<0,001). There was no statistically significant relationship with tumour mutation burden, total neoantigen or survival status. PRAME expression was positively correlated with CD8+ T cells and follicular helper T cells infiltration and negatively correlated with CD4+ T cells, regulatory T cells, neutrophils, mono- cytes, CAFs and endothelial cells (p<0,05). The analyses performed with TISIDB and GEPIA2 showed that PRAME expression was negatively correlated to the expression of many immune checkpoint genes (PDCD1, PDCD1LG2, TIGIT, CD274, CTLA4, HAVCR2, LAG3) (p<0,001). Conclusion: PRAME expression was associated with immune infil- tration and immune modulator or immune check points genes. Our results suggested that it can be a potential biomarker for predicting immunotherapy response in melanoma. PS-08-002 Genetic and epigenetic changes in melanoma progression: a TCGA based study Y. Cakir*, M.H. Toper, B. Lebe, S. Sarıoğlu *Dokuz Eylül University, The Institute of Health Sciences, Department of Molecular Pathology, Turkey Background & objectives: We aimed to investigate molecular mecha- nisms affecting melanoma progression by comparing genetic/epigenetic features between melanoma having different Breslow thicknesses and stages via TCGA data. Methods: Data were collected from “cBioPortal” bioinformatic ser- vice. Cases having complete information were included, metastatic cases were excluded. Cases were compared in terms of copy number variations (CNV), DNA mutations, mRNA/protein expression, agnos- tic biomarkers (tumour mutation burden, NTRK, HER2, NRG, RET, BRCA, KRAS, FGFR). Gene set enrichment analysis were performed with g:Profiler. p and q<0.05 were accepted as statistically significant. Results: Breslow thickness was ≤1mm in 41 cases, >1mm in 159 cases. 230 and 34 differentially expressed genes were detected in thin and thick melanomas, respectively. g: Profiler analysis showed that these genes have roles in immune response/regulation and keratinocyte differentiation, respec- tively. 10 genes were hypermethylated in thick melanomas. T stages were; Tis:7, T1:27, T2:62, T3:57, T4:51. In Tis, 252 genes had significant CNV, 147 and 3 genes showed DNA mutation with higher fre- quency in Tis and T1, respectively. Hypermethylation was detected for a gene in T1 and T3; 7 genes in Tis. One gene (OR10G3) had higher mRNA expression in Tis (p,q<0,05 for genes mentioned). Other parameters weren’t statistically significant. Conclusion: Melanoma progression is a complex process comprising many genetic/epigenetic changes. Understanding these changes is essen- tial for diagnosis and predicting melanocytic lesions’ prognosis. Our results can light subsequent studies to identify the steps in melanoma progression. PS-08-003 Feasibility and impact of embedding a larger DNA and RNA tis- sue-based sequencing panel for the routine care of patients with advanced melanoma in Spain A. Carrasco Lorenzo*, N. Castrejon, M. García, M. Marginet, P. Jares, C. Montironi, J. Navarro, A. Arance, L. Alos, C. Teixido *Department of Pathology, Hospital Clinic, IDIBAPS, University of Barcelona, Spain