ECP 2023 Abstracts

S355 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 Further, the clinical course of the patients was compared with all the findings. Results: Characteristic histological and immunohistochemical fea- tures were observed in all cases in our series. EWSR1 rearrangement was found to be positive in 7 of 9 cases studied. Mild atypical cells were observed in only 1 of 13 cases in our series, and no prognostic difference was found between this case and the others. Three cases showed pseudovascular spaces in the nodules and a fibrous capsule with inflammatory cells, particularly prominent secondary follicles in some areas, which raised suspicion of metastasis. At the time of diagnosis, metastasis to the lung was found in 1 of 2 cases located in the lower extremity, and lymph node metastasis was found in the other case. Conclusion: As distinct from the literature, lung metastasis was detected for the first time in our series. The diagnosis of angio- matoid fibrous histiocytoma is difficult due to its rarity, pattern diversity, and the absence of a specific immunohistochemical marker. Although the risk of metastasis and death rates are low, correct diagnosis is extremely important. Recently identified gene fusions are the most important diagnostic indicators for a defini- tive diagnosis. E-PS-22-010 Molecular identification of an intra-thoracic BCOR‐rearranged sarcoma with novel BCOR‐CLGN gene fusion Y.C. Chang Chien*, K. Madarász, S.L. Csoma, J.A. Mótyán, H. Huang, A. Mokánszki, G. Mehes *University of Debrecen Clinical Center Institute of Pathology, Hungary Background & objectives: BCOR ‐ rearranged sarcomas (BRS) are a heterogeneous entity previously classified as “atypical Ewing” sar- comas with histopathological similarities which make diagnosis chal- lenging. The most common aberrations are CCNB3 fusion and BCOR ITD. Various new fusion partners have been reported, further increase its complexity. Methods: We present a case of intra-thoracic tumour from a 52 ‐ year ‐ old female patient with clinical impression of metastatic carcinoma from endometrium. Morphological evaluation was performed, followed by immunohistochemistry (IHC) studies, fluorescence in situ hybridiza- tion (FISH), next generation sequencing (NGS) and Sanger sequencing. In silico protein analysis was also carried out to demonstrate the 3D structure of the chimeric protein. Results: A 52 ‐ year ‐ old female patient with history of endometrioid adenosarcoma (grade 2) revealed a right ‐ side chest wall tumour during follow up with costal and pleural invasion. The tumour cells showed typical small, round-spindle morphology resembled Ewing sarcoma with positivity for CD99(diffuse to patchy), INSM1, NKX2.2, TLE1, SATB2 and BCOR by IHC. Further molecular anal- ysis identified BCOR gene translocation by FISH. BCOR (exon 15) and CLGN (exon 9) gene fusion was found by NGS and confirmed by Sanger sequencing. In silico protein analysis showed the protein product of the BCOR ‐ CLGN is composed of full-length BCOR protein and N-terminal signal sequence of calmegin (protein prod- uct of CLGN gene) was missing, which hampered the intracellular translocation. Conclusion: We report the first case of BRS with a novel CLGN fusion which shared morphological and immunophenotypical sim- ilarities with other fusion variants, which contribute to the con- tinued expanding molecular subtype of BRS. Molecular ancillary tests, such as NGS and confirmatory Sanger sequencing, serve as powerful tools to discover these rare variants. In addition, the in silico analysis of the BCOR ‐ CLGN fusion protein is an appropriate approach to better understand the pathogenesis by evaluating the fusion protein’s characteristics. E-PS-22-011 Rare tumour with uncommon clinical behaviour: relapsed intra- muscular angioma of the elbow A. Ciongariu*, A. Dumitru, M. Sajin, A. Marin, M. Costache *Department of Pathology, University Emergency Hospital Bucharest, Romania Background & objectives: Intramuscular angioma is an exceptionally rare neoplasm arising in skeletal muscle. It typically affects young patients and frequently develops in the upper extremities. Although considered a benign tumour, incomplete surgical resection followed by relapse may lead to a difficult diagnosis. Methods: We present the case of a 28-year-old male who developed a large, rapidly growing, soft tissue tumour of the upper limb and underwent surgical excision, followed by relapse. Considering the aggressive clinical behaviour of his lesion, a malignant proliferation was suspected. Surgery was carried out and a frozen section was per- formed during the procedure, suggesting the diagnosis of intramuscular angioma. Results: Microscopic examination revealed a benign tumour prolifera- tion consisting of endothelial cells lacking atypia and mitotic figures, forming variable-sized vascular spaces, with occasional plexiform architecture. The lesion was poorly defined and displayed vascular structures and chords dissecting the adjacent striated skeletal muscle fibres. Upon immunohistochemical analysis, we identified strong ERG, CD31 and CD34 expression within the tumour cells. Ki 67 proliferation marker was expressed within 1% of tumour cells. Expression of S-100, HHV8 and MDM2 was absent in the proliferated elements. The diagno- sis of intramuscular angioma was confirmed. However, the tumour pro- liferation extended close to the surgical resection margins and thorough correlations with the surgical and clinical data were recommended. Conclusion: Intramuscular angioma can be a challenging diagnosis, considering the peculiar permeative growth pattern and unusual clini- cal behaviour of this proliferation. Management of this entity requires increased attention during microscopic examination and should be completed by immunohistochemical analysis. We also emphasize the importance of adequate examination of the surgical resection margins, to prevent relapses and inappropriate treatment. As a result, knowledge and awareness in the matter of this condition is crucial in order to avoid misdiagnosis, especially considering its rarity. E-PS-22-012 Epithelioid neoplasm with EWSR1/FUS-CREB fusions and predi- lection for mesothelial-lined cavities: case report A.P. Diazgranados Daza*, T.M. Silva, G. Tapia Melendo, J. Chabla Jaramillo, J. Garcia Gomez, S. Ramón y Cajal Agüeras, C. Romagosa Perez-Portabella *Hospital Vall D’Hebron, Spain Background & objectives: Recently a case series describing a group of tumours with predilection for mesothelial-lined cavities showing epi- thelioid morphology has been reported; co-expression of citokeratines/ WT1, negativeness of calretinine and EWSR1/FUS-CREB fusion genes presence. We report a case of this potential novel entity. Methods: We report a case of a 43-year-old male patient admitted to the hospital for fever and anaemia. The CT scan showed a solid mediastinal subcarinal and right hilar mass (65x45mm). The patient underwent a thoracoscopy for pleural and mediastinic mass biopsy. We analyse the histological sections, carry out immunohistochemistry and molecular analysis by next-generation sequencing (NGS) “Archer FusionPlex Expanded Sarcoma”. Results: The histopathology examination revealed a fibrous-looking tissue with myxoid degeneration and cystic changes, infiltrated by a proliferation of monotonous small/epithelioid cells arranged in nests, trabeculae and cords-like. Tumour cells show round nuclei, sometimes