ECP 2023 Abstracts

S79 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 Background & objectives: Targeted NGS allows a fast and efficient multi-gene analysis in melanoma. The main objective of this study is to describe the genetic alterations of melanoma cases using an NGS DNA and RNA panel, relating these results with the clinicopathological features. Methods: Patients diagnosed with advanced melanoma at our cen- tre from 2020 to 2022 were included. Total genomic DNA and RNA were extracted from formalin-fixed and paraffin-embedded samples for sequencing. Results: A series of 87 advanced melanoma cases were selected for the study. The most prevalent mutated genes were BRAF (29%), NRAS (28%), ALK, KIT, and MAP2K1 (5% of each three). Co-occurrence of oncogenic mutations was detected in 24/82 (29%) of the samples, such as BRAF with CTNNB1, EGFR, ALK, HRAS, and MAP2K1; and the combination of NRAS with IDH2, IDH1, KIT, and JAK2. Amplifica- tions and rearrangements were detected in 4 cases (5%). Significant statistical association between BRAF mutation and sun exposition was found. However, no other significant statistical associations were identified. Conclusion: Targeted NGS testing is an essential tool in advanced mela- noma patients’ evaluation since it provides complete molecular genetic information required for their proper therapeutic management. This expanded knowledge about the molecular alterations of advanced mela- noma could underlie the development of new effective targeted treatments. PS-08-004 Clinicopathological features, cell cycle regulators and Ki 67 in der- matofibrosarcoma protuberans M.S. Chang*, S. Byeon, S. Park, S. Yoo, C. Lee *Seoul National University College of Medicine, Boramae Hospital, Republic of Korea Background & objectives: Little is known about cell cycle regulators in dermatofibrosarcoma protuberance (DFSP). We aimed to determine key variables for adverse outcome of patients with DFSP. Methods: We reviewed clinicopathological features for 127 cases of DFSPs having wide local excision with clear resection margin. Immu- nohistochemistry was conducted for p53; cyclin D1/cyclin-dependent kinase (CDK)4 and cyclin E/CDK2 as cell cycle activator; p16INK4A and p21CIP1 as CDK inhibitors; phospho-retinoblastoma (pRB), and Ki67 (a proliferation marker). Results: Compared to 97 non-recurrent DFSPs, 30 recurrent DFSPs revealed a predilection for head and neck in location, larger tumour size, deeper invasion beyond the subcutis, more frequent mitotic fig- ures, more diverse histologic subtype, and more frequent CDK4+ and combined CDK4+/p16INK4A-. Four metastatic DFSPs (three of fibro- sarcomatous type and one of myxoid type) disclosed nil, one, four or eleven instances of local recurrence. Metastatic DFSPs showed larger tumour size, deeper invasion beyond the subcutis, and more frequent mitotic figures than non-metastatic DFSPs. Cyclin D1 and Ki67 expres- sion tended to differ from “low” in primary skin lesion to “high” in corresponding metastatic sites. None of 127 DFSPs presented p53 overexpression. Conclusion: CDK4+ and p16INK4A- in tumour cells may be useful as biomarkers predicting local recurrence of DFSP. Cyclin D1 and Ki67 may be associated with DFSP progression, and further, metastasis. p53 may be not involved in development of DFSP. Funding: Basic Science Research Program through The National Research Foundation of Korea, funded by the Ministry of Education under award number 2016R1D1A1B01010316. PS-08-005 Analysis of the corelations between PRAME expression and mela- noma subtypes A. Georgescu*, T. Georgescu, M. Sajin, F. Pop *Department of Pathology, "Carol Davila" University of Medicine and Pharmacy Bucharest, Department of Pathology, Nephrology Clinical Hospital "Dr. Carol Davila", Bucharest, Romania Background & objectives: Preferentially Expressed Antigen in Mela- noma (PRAME) is an antigen from the Cancer testis family, normally expressed in the gonads, which has been proved to be expressed in different malignant lesions and which is now widely used to immuno- histochemically identify melanoma. Methods: We have reevaluated 59 cases of cutaneous melanoma (3 lentigo maligna melanoma, 5 acral melanoma, 12 nodular melanoma, 34 low-CSD melanoma and 5 Spitz melanoma) which were diagnosed between June 2021 and December 2022. PRAME immunoreactivity has been evaluated using a 4-tiered grading system, incorporating both intensity and percentage of positive cells. Collected data has been ana- lysed using SPSS software. Results: PRAME immunoreactivity strongly correlated with the sub- types of melanoma (p=0,003), with all lentigo maligna melanoma as well as acral melanomas, showing strong and diffuse immunoreactivity for PRAME (4+). 66,6% of all nodular melanoma showed a 3+ pat- tern of PRAME immunoreactivity, while the other 33,3% displayed 4+ immunoreactivity. Regarding low-CSD melanoma, the distribution of the patterns of immunoreactivity was most diverse, with 14,7% show- ing pattern 2+, 47,05% showing pattern 3+ and 38% showing pattern 4+. Regarding Spitz melanoma, pattern 4+ was observed in 20% of all cases and 60% showed pattern 3+, while the remaining showed no immunoreactivity for PRAME (adequate on-slide control was present in sebaceous glands). Conclusion: In conclusion, 100% of all acral melanomas and lentigo maligna melanomas showed diffuse and strong immunoreactivity for PRAME melanoma, with a statistically significant correlation between the histopathological subtype of melanoma and PRAME immunore- activity. The most variable pattern of expression was observed in low- CSD melanoma, which also represented the most common subtype of malignant melanoma in our study. A pattern of immunoreactivity of 3+ and 4+ was observed in 89,84% of all malignant melanomas included in our database. PS-08-006 The role of PRAME for the differential diagnosis between nevus with regression-like fibrosis/sclerosing nevus with pseudomelano- matous features and its malignant mimickers A. Orsatti*, B. Corti, F. Ambrosi, E. Dika, M. Lambertini, M. Grillini, A.A.P. De Leo, M. Fiorentino, C. Ricci *Pathology Unit, IRCCS Azienda Ospedaliero-Universitaria di Bolo- gna, University of Bologna, Bologna, Italy, School of Anatomic Pathol- ogy, Department of Biomedical and Neuromotor Sciences, University of Bologna, Italy Background & objectives: Nevus with regression-like fibrosis/ sclerosing nevus with pseudomelanomatous features (NRLF/ SNPMF) is a clinical and histologic simulator of well-defined mel- anoma (M) histotypes. Herein, we tested PRAME for the differen- tial diagnosis between NRLF/SNPMF and its malignant mimickers. Methods: We retrospectively collected 20 NRLF/SNPMF and 25 M mimickers, namely 11 M with extensive regression of fibrous- type (MERF), 7 recurrent M (RM), and 7 nevus-associated M (NAM). We adopted a double stain (DS) for Melan A/PRAME and the score 4+ sec. Lezcano C et al. (≥75% of positive nuclei) has been chosen to dichotomize the cases in positive and negative. Results: The sensitivity (SE), specificity (SP), and accuracy (AC) of PRAME for the distinction of NRLF/SNPMF from the glob- ally- and singly-evaluated M histotypes were: all M mimickers (SE: 76%, SP: 100%, AC: 86.6%), MERF (SE: 90.9%, SP: 100%,