ECP 2023 Abstracts

S99 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 Results: Out of 7 cases of CCC, 6 were males and 1 was female. Five cases occurred in femur, one in humerus and one in vertebral body. All these cases were diagnosed a benign lesion on radiology and turned out to be malignant CCC on histology. Two of these cases had aneurysmal one cyst-like areas. Immunohistochemistry was done in 2 cases. Bone curet- tage with grafting was done in all cases, followed by wide local excision in three cases. There is no evidence of recurrence or metastasis in these patients till the last follow up. Conclusion: Clear cell chondrosarcoma almost always mimics a benign lesion clinically and radiologically, with a mortality rate of 15% and metastatic potential of 20% in 10 years. We emphasize the importance of clinical, radiological and pathological integration to diagnose this lesion and always look out for the clear cells on patho- logical examination, when one comes across a clinical diagnosis of benign lesions such as chondroblastoma, giant cell tumour or aneurys- mal bone cyst in slightly older patients. PS-14-007 Data analysis of synovial specimens in a Portuguese tertiary centre – prevalence, diagnostic and prognostic significance M. Pinho Fialho*, C. Ochôa Matos, V. Fernandes, R. Moiteiro da Cruz, J. Boavida, E. Vieira-Sousa, M.E. Vitorino, R. Luís *Serviço de Anatomia Patológica, Centro Hospitalar Universitário de Lis- boa Norte, Faculdade de Medicina da Universidade de Lisboa, Portugal Background & objectives: Joint pathology encompasses a broad group of diseases, often with overlapping features. Our aim was to assess whether the histopathological study of synovial samples could complement suspected clinical diagnoses or clarify therapeutic failure scenarios, allowing for a precise management. Methods: We analysed the reports of all synovial specimens received at our Department between 2010-2022. The specimens were mainly submitted for diagnosis and/or management guidance, especially in the context of therapeutic failure. Clinical and histological diagnoses were both categorized into tumour-like, degenerative/non-inflammatory and inflammatory lesions, further subclassified by the Krenn score; the categories were then matched for comparison. Results: A total of 599 reports pertaining to 535 patients (335 female, 264 male; 0-93y.o.) were reviewed. Most specimens were collected by the Rheumatology and Orthopedics Departments. Histologically, the samples were classified as low-grade synovitis (36%), high-grade synovitis (15%, with 5% further established as rheumatoid arthritis), septic arthritis (10%), microcrystalline arthritis (3%) and granuloma- tous synovitis (3%); tumour-like lesions were diagnosed in 18%, mainly encompassing cysts (10%); the remainder were mostly non-informative. Clarification of clinical diagnosis and/or differential diagnosis was possible in the majority and in some cases, microscopic evaluation gathered unforeseen information, allowing for a definitive diagnosis of immune-related, septic, granulomatous and microcrystalline arthritis or revealing (pseudo)tumoral lesions. Conclusion: Synovial histopathological evaluation may benefit patients in select cases, namely when a clinical differential requires clarification or, after a diagnosis is established, a secondary diagnosis or infection must be excluded. Nevertheless, integration of clinical, laboratorial, radiological and histological data through multidisciplinary discussion is the ultimate approach to improve patient care. PS-14-008 A retrospective analysis of 116 patients with chordoma: morpho- logic and clinical characteristics M. Ramadwar*, S. Lashkar, N. Khanna, D. Sharma, B. Rekhi, P. Panjwani, V. Raje, M. Patel, M. Pruthi, P. Nayak, A. Janu *Tata Memorial Hospital, India Background & objectives: Chordoma is a malignant tumour of noto- chordal origin arising in sacrococcygeal or clival region. Histologic variants of chordoma are associated with different biologic, morpho- logic and clinical characteristics. We aim to study the histopathologi- cal spectrum of chordoma along with clinical features. Methods: We studied 116 patients diagnosed with chordoma. Clini- cal features including treatment details and follow up information were derived from electronic medical records. Histopathology and immunohistochemistry were reviewed. Results: 116 patients with chordoma had age range of 1 to 75 years. Sacrococcygeal region was the commonest site followed by base skull. Conventional morphology was seen in 88% while poorly dif- ferentiated chordomas (PDC) were seen in 8.6% patients. Dediffer- entiation was seen in 1.6%. All tumours were positive for brachy- ury, EMA and S100. All PDCs contained rhabdoid cells with loss of INI1. 27% patients underwent surgery, 44% patients had radio- therapy, 22% were treated with combination therapy. 41% patients had incomplete surgical resection. None of the patients had com- plete response to radiotherapy. 5 patients died of disease; 3 were patients with PDC. 16% patients experienced disease relapse; 3 had metastases. Conclusion: Results of our study of 116 patients have highlighted chordomas as aggressive malignant tumours with bulky, locally destructive tumours. They were refractory to therapy with high rates of incomplete surgery, poor control on radiotherapy and high relapse rates. Sacrococcygeal site was the commonest. A consistent morphologic and immunohistochemistry profile was observed with brachyury being highly specific marker for notochordal differentia- tion. PDCs emerged as distinctive tumours showing rhabdoid phe- notype and loss of INI1. Aggressive behaviour of PDCs was also clearly evident. PS-14-009 Fusion gene rearrangements in nodular fasciitis: a study of rare and novel USP6 fusion partners J. Zamecnik*, J. Balko, M. Stanek, L. Krskova *Department of Pathology and Molecular Medicine, 2nd Faculty of Medicine, Charles University and Motol University Hospital, Prague, Czech Republic Background & objectives: In this retrospective non-randomised study we aimed to identify new and rare fusion partners with USP6 gene in nodular fasciitis. Nodular fasciitis can harbour different variants of USP6 fusions, which can be used in diagnostics and determine the biological behaviour. Methods: A total of 19 cases of nodular fasciitis examined between 2011 and 2022 at Motol University Hospital in Prague, Czech Republic were enrolled into this study. Next to the histopathologi- cal evaluation, all cases were assessed using immunohistochemis- try, RT-PCR and Anchored multiplex RNA methods. Patient’s main demographic characteristics and corresponding clinical data were also analysed. Results: This study presents one novel ( KIF1A ) and five rare exam- ples ( TMP4, SPARC, EIF5A, MIR22HG, COL1A2 ) of fusion partners with USP6 gene among the 19 cases of nodular fasciitis. Conclusion: Identification of USP6 fusion partners in nodular fas- ciitis helps to understand the biology of the lesions. Moreover, it can be useful in routine histopathological practice of soft-tissues diagnostics, especially in preventing possible misdiagnosis of malignancy. Funding: Research Project of the Ministry of Health of the Czech Republic No. 00064203.