ECP 2022 Abstract Book

Virchows Archiv (2022) 481 (Suppl 1):S1–S364 13 Conclusion: MS is rare disease with a sporadic character, benign, but gradually disabling course. Affects both sexes. The first mani- festations occur in childhood. True venous malformations and hemangioendotheliomas appear on the skin. The second most important clinical sign is the bone deforming enchondroma. MS represent a medical and social problem, which implies the impor- tance of the task of choosing the tactics of treatment of patients with such a disease. E-PS-22-033 Poorly differentiated chordoma, a rare type of chordoma, in a 2.5-year-old girl M.M. Savas*, I. Tosun *Umraniye EducationTraining Hospital, Turkey Background & objectives: Chordoma is a relatively rare locally inva- sive and potentially malignant tumour of foetal notochord. Poorly dif- ferentiated chordoma (PDC) is a rare type of chordoma. In the most cases with PDC, cytogenetic studies identified deletions in SMARCB1, a tumour suppressor gene. Methods: We report an exceptional case of a late local failure of a PDC of the cranio-cervical junction in a 2.5-year-old girl. The patient was admitted to the hospital with complaints of tender- ness and limitation of movement in her neck. MRI and PET/CT revealed a tumour infiltrating C1 vertebra, compressing spinal cord and conglomerated metastatic lymphadenopathy in the left supraclavicular area. Results: On histological examination, tumour was composed of multinodular sheets of cells in mostly epithelioid and scat- tered sarcomatoid morphology with eosinophilic cytoplasm and prominent pleomorphism. The nuclei were round to ovoid, with vesicular chromatin and mitotic activity was increased. Necro- sis was present. The physaliphorous cells typical of chordoma with classic features were absent. Immunohistochemistry stain- ing revealed that the cells were reactive for panck, brachyury; nonreactive for s100, myogenin, myod1, desmin, CD99, CD34 and SMARCB1(INI1) expression was found to be lost. Loss of SMARCB1 protein expression has recently been identified in a variety of tumour types such as PDC and malignant rhabdoid tumours (MRT) including atypical teratoid/rhabdoid tumour. Conclusion: Although the histological and clinical features of PDC resemble MRT, brachyury and cytokeratin immuno-expressivity may help to distinguish PDC from those. PDC is a newly recog- nized entity in the recent World Health Organization classification of tumours of soft tissue and bone. Treatment consists of a com- bination of surgery and chemo-radiotherapy. Fewer than 60 cases have yet been reported in the English literature and this rare-type of chordoma, PDC, is associated with poor prognosis that worse than conventional chordoma. E-PS-22-034 Whole exome sequencing analysis of dedifferentiated chondrosarcoma J. Schreier*, A. Roessner, S.R. Ullmann, D. Schanze, D. Jechorek, S. Franke *OvGU Magdeburg Department of Pathology, Germany Background & objectives: Dedifferentiated chondrosarcoma (DDCS) is a biphasic malignant mesenchymal tumour with a low malignant component equal to chondrosarcoma grade 1 and a highly malignant component resembling pleomorphic sarcoma. Studies comparing genetic alterations of these components using whole exome sequenc- ing are rare. Methods: In our study DNA was extracted from formalin-fixed, paraffin-embedded tissue samples. After thorough quality check- ing, the DNA samples were analysed. For an improved understand- ing of the molecular genetic differences in DDCS, whole exome sequencing of 5 tumours with 2 samples each, was used to compare the genetic landscape of paired conventional and dedifferentiated tissue components. Results: In line with recent publications IDH1/2 mutations could be observed in both tissue components of several samples. While alterations in the COL2A1 gene (Collagen Type II Alpha 1 Chain) were found in both components, we also discovered broad altera- tions of different collagen type genes. Mutations in the TP53 and TP53BP1 gene could be found in both portions. Interestingly alter- ations within the CD4/CD6 pathway were found predominantly in the dedifferentiated tissue. Moreover Wnt/β-catenin and hedge- hog pathway mutations as well as TERT promoter mutations were observed along with a broad spectrum of alterations in APOB, ATRX, BRCA, GLI1/2, SOX9 and chromatin regulatory genes. Conclusion: Our results confirm the detection of IDH1 and IDH2 mutations in both tissue components. This points to a monoclo- nal origin of DDCS. Furthermore, our findings confirm an estab- lished pattern of particular mutations in important driver genes, like CDKN2A, BRCA, KIT. Exploring extensive mutations in the CD4/CD6, Wnt/β-catenin and hedgehog pathways could lead to advances in possible targeted therapies. E-PS-22-035 Pseudomyogenic Hemangioendothelioma in the thumb – report of a rare case F. Sousa Vieira*, D. Sá, A. Coelho, J.R. Vizcaíno *Centro Hospitalar Universitário do Porto, Portugal Background & objectives: Pseudomyogenic hemangioendothe- lioma is a rare soft tissue tumour, mostly indolent and infrequently metastasizing. It usually presents with multiple cutaneous nodules in extremities, mainly affecting young adults. Due to its relative uncom- monness and unusual presentation, this tumour can be diagnostically challenging. Methods: We report a multifocal PMHE in the left thumb of a 41-year-old man. The patient described painful lesions, and three tumours were confirmed by MRI, located in the thenar eminence, proximal phalanx and subungual area. He was submitted to a distal amputation through the interphalangeal joint and a separated resection of the proximal tumour, resulting in symptomatic relief. Results: Histopathological examination of the resected specimens revealed multiple foci of a mesenchymal neoplasm of high cellularity, consisting of short fascicles of spindled and epithelioid cells with low pleomorphism, with ample and eosinophilic cytoplasm, vesicular nucleus and evident nucleolus. The neoplasm had no necrosis, had low mitotic index and was permeated by neutrophils. The growth pattern was infiltrative, with skeletal muscle tissue and bone invasion. Immunohistochemistry was performed in sections of both soft tissue component and bone-infiltrating component (with decalcifying procedure). The tumour cells were immunoreactive for CD31, ERG, AE1/3, CAM5.2 (focal) and INI1 (preserved). In the decalcified sample, however, the nuclear staining of INI1 and ERG were equivocally weak. Conclusion: With the described findings, the diagnosis of pseudomyogenic hemangioendothelioma was made. The decalcification procedure, however, can cause misinterpretation S345