ECP 2022 Abstract Book

Virchows Archiv (2022) 481 (Suppl 1):S1–S364 13 local response. CD30+ LPD and PLEVA may show similar histo- pathological patterns and may be difficult to differentiate without clinical data on small biopsies and GATA3 expression may be a clue for diagnosis. PS-12-010 NTRK fusion in pigmented spindle cell nevus/Reed nevus: an immunohistochemical study on a large multicentric Italian cohort C. Ravaioli*, F. Ambrosi, M. Lambertini, B. Corti, M. Fiorentino, G. Tallini, D. De Biase, E. Dika, C. Ricci *School of Anatomic Pathology, University of Bologna, Italy Background & objectives: Pigmented spindle cell nevus/Reed nevus (PSCN/RN) is a Spitz nevus variant genetically characterized by NTRK (mainly NTRK3) gene fusions, but the data about the fre- quency of this genomic alteration are widely discordant and range from 14 to 52%. Methods: All PSCN/RN diagnosed at our institutions (February 2017-December 2021) were collected and stained with pan-TRK antibody (EPR17341; rabbit monoclonal; Ventana, OptiView RED Detection Kit). We evaluated the percentage of positive cases and analysed the association between pan-TRK(+) and other clinical- pathological features [ χ 2 tests for dichotomous and categorical data; Student t-test (normal distribution) and Mann-Whitney U-test (non-normal distribution) for continuous data]. Results: A total of 44 PCSN/RN were collected and histologi- cally confirmed, according to 2018 WHO Classification of Skin Tumours. pan-TRK(+) was detected in 6 (13.6%) cases and exhib- ited a specific expression pattern [cytoplasmatic, granular, dif- fuse (4/6, 67%) or not (2/6, 33%)]. pan-TRK(+) was significantly associated with localization [4/6 (67%) on trunk/dorsum and 2/6 (33%) on extremities, p=0.008] and cytological atypia [1/6 (17%) mild, 2/6 (33%) moderate and 3/6 (50%) high, p=0.004]; no other clinical-pathological features were significantly associated with pan-TRK(+). Conclusion: This is the largest case series of PSCN/RN tested for NTRK fusions. We found that a subgroup of PSCN/RN is char- acterized by NTRK fusions, with a percentage of positive cases (13-14%) similar to what was previously shown by Kervarrec T. et al. Furthermore, we found that PSCN/RN pan-TRK(+) are pref- erentially localized on trunk/dorsum and extremities, and display moderate/high cytological atypia. We will integrate our data with molecular techniques to support our results and better compare them with previous studies. PS-12-011 Approaching the cellular origin of Merkel cell polyomavirus (MCPyV) associated Merkel cell carcinomas: effects of MCPyV Gene expression in epithelial and lymphoid cells A. Macamo*, D. Liu, M. Färber, F. Borman, E. Speel, V. Winnepenninckxs, F. Klufah, E. Chteinberg, A. zur Hausen *Department of Pathology, GROW-School for Oncology & Devel- opmental Biology, Maastricht University Medical Center+, The Netherlands Background & objectives: Merkel cell carcinoma (MCC) is a rare but deadly non-melanoma skin cancer. Although there is accumulating of evidence that Merkel cell polyomavirus (MCPyV) contributes to the etiopathogenesis of MCC, the cell of origin of MCC remains elusive. Methods: We stably introduced MCPyV small and large tumour antigens in two MCPyV-negative cell lines, an epithelial and a leukaemia B-cell line and compared the gene expression changes induced thereafter. We assessed the MCPyV effects through func- tional and pathway enrichment analysis of MCPyV-T antigens expressed in the cell lines with immunological and neurological terms and validated their expression in primary MCCs. Results: The results revealed that in the epithelial background, the global effects of MCPyV T antigens are higher compared to the lymphoid background, mainly attributed to the higher differential expression of genes caused by the LT antigen. Genes upregulated by MCPyV sT antigen were associated with neurological gene- ontologies in both cell lines. Key genes in neuronal development, differentially expressed in the lymphoid background were enriched in pathways that have been implicated in human cancers such. Validation of significantly enriched genes was assessed in the primary MCC cell lines and tumours, of which all genes were highly expressed, suggesting the involvement of MCPyV T antigens in regulating neuronal pathways involved in tumorigenesis. Conclusion: We conclude that the expression of MCPyV T anti- gens in epithelial and lymphoid background affects neurological pathways in both. However, more effects are seen by the introduc- tion of sT antigen expression in the lymphoid background. These novel established cell lines comprise an important tool to study the cell of origin of MCPyV- associated MCCs. PS-12-012 Micromorphometric parameters of B16 melanoma cells and their circadal Y. Kirillov, A. Borisov, M. Kozlova, L. Makartseva, S. Timofeev*, E. Rusina, D. Areshidze *Moscow MCC Kommunarka, Russia Background & objectives: Violation of the circadian rhythm is a risk factor for the development of melanoma. Tumours are also charac- terized by a change in the normal daily rhythm. Micromorphometric parameters of B16 melanoma cells and their circadian rhythms were investigated. Methods: The study was conducted on 50 male BDF1 hybrid mice divided into 2 equal groups. First - control, mice of the second group were transplanted with B16/F10 melanomas. On the 15th day, the animals were withdrawn from the experiment at 9.00, 15.00, 21.00 and 3 hours. Conducted studies of micromorphometric parameters of tumours and their daily dynamics using cosinor analysis. Results: It has been established that atypical melanocytes are characterized by significantly larger nuclei with a decrease in its elongation and contour indices with an increase in the shape factor. Daily fluctuations in the size of the nucleus of tumour cells are of a significant circadian nature, with acrophase rhythm of 7^24 in the control and 4^12 in the experiment at amplitudes of 1.48 and 4.52 sq.μm, respectively. The tumour cell size circadian rhythm was characterized by an acrophase in 19^32 and an amplitude of 10.07 sq.μm . According to the cosinor analysis, for the nucleo- cytoplasmatical ratio, circadian rhythm was not significant. Conclusion: The data obtained indicate a change in rhythmosta- sis in mice with experimental melanoma B16. The features of the organization of the rhythm of the tumour itself can be used in its targeted experimental therapy, taking into account chronobiological features. The results of the study can be used for further studies of the effect of various lighting modes on the morphofunctional state of the animal organism in the pathology under study. PS-12-013 S132