ECP 2023 Abstracts

S353 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 Conclusion: P63 is a helpful marker for diagnosing giant cell tumours of bone due to its high sensitivity. However, it cannot be recommended as the single definitive test for making this diagnosis. The results need to be carefully interpreted in conjunction with other diagnostic methods such as imaging studies. E-PS-22-003 Dedifferentiated liposarcoma in a spindle cell rhabdomyosarcoma: a rare and complex case F. Almarii*, A. Procop, T. Radaschin, C. Vasilescu, V. Herlea *Fundeni Clinical Institute, Centre of Excellence in Translational Med- icine, Fundeni, University of Medicine and Pharmacy "Carol Davila" Bucharest, Romania Background & objectives: Dedifferentiated liposarcoma(DDLPS) and spindle cell rhabdomyosarcoma(SCRMS) are rare subtypes of soft tissue sarcomas, each with their own unique histopathological and molecular characteristics. Association of the two has rarely been described, making the diagnosis and management of these cases par- ticularly challenging. Methods: We present the case of a 63 years old female diagnosed and treated in Fundeni Clinical Institute. She was diagnosed with retrop- eritoneal liposarcoma in May2022 and while pursuing chemotherapy, the radiologic team described a 13.6 cm tumour in the left infrarenal compartment and surgical approach was proposed. We received a large whitish grey tumour, with cystic, myxoid and necrotic areas. Results: The tumour consisted of a well-differentiated liposarcoma component (WDLS) juxtaposed with a non-lipogenic, high-grade sar- comatous component, characterized by round and elongated, spindle- shaped tumour cells with eosinophilic cytoplasm and peripherally placed pleomorphic nuclei, arranged in a fascicular or storiform pat- tern, with a prominent vascularization, necrosis, frequent mitoses and vascular invasion. On immunohistochemistry, the cells were diffusely positive for MDM2, CD99 and MyoD1, were focally positive for smooth muscle actin and were negative for S100 and AE1/AE3. This case was signed out as a dedifferentiated liposarcoma with a spinde cell rhabdomyosarcomatous transformation, grade 3 FNCLCC, with vascular invasion, located in the retroperitoneum. Conclusion: Dedifferentiated liposarcoma in a spindle cell rhabdo- myosarcoma represents a rare and complex presentation of soft tissue sarcoma, posing significant challenges in diagnosis and management. The accurate identification of both components within the same tumour is crucial for determining the appropriate treatment strategy and pre- dicting prognosis. Further research is needed to better understand the molecular mechanisms underlying the co-occurrence of DDLPS and SCRMS and to identify potential therapeutic targets for this rare and aggressive form of sarcoma. E-PS-22-004 Histopathological and clinical features of pelvic chondrosarcomas B. Altuntaş Keskin*, S.A. Arsoy, A.M. Onenerk Men, M.K. Ozsahin, H.F. Dincbas, C. Comunoglu, N. Çomunoğlu *Istanbul University-Cerrahpasa, Cerrahpasa Medical Faculty, Pathol- ogy Department, Turkey Background & objectives: Pelvic chondrosarcomas are primarily treated with surgery with wide margins. These tumours show frequent local recurrence and distant metastasis. We aimed to present histo- pathological features and clinical outcomes of our case series of pelvic chondrosarcomas. Methods: A total of 60 pelvic chondrosarcoma cases diagnosed between 1998-2022 in three hospitals (Istanbul Cerrahpaşa Univer- sity, M. Sabancı Baltalimanı Hosp. and Prof. Dr C. Taşçıoğlu Ş. Hosp.) were retrospectively analysed. Clinical and histopathological features were examined. Results: Thirty-nine cases were male and 21 were female. Mean age at the diagnosis was 52,6 (ranging between 18-91). Thirty-nine cases were located at iliac bone, 1 at ischium, 5 at acetabulum and 9 at sacrum. In 23 patients, local recurrence occurred. In 3 patients, metastasis was detected. Twenty-eight patients died of disease. Twenty-three cases were grade 1 and 37 cases were grade 2 or 3. Conclusion: Pelvic chondrosarcomas are mostly high grade highly malignant tumours having poor prognosis with high recurrence and mortality rates, and they are difficult to treat. E-PS-22-005 A case report of a 25 year old woman with a known history of biphasic synovial sarcoma and a late recurrence in the retroperi- toneal space E. Baliou*, M. Christidis, E. Bairamidis, D. Nikolakopoulos, M. Pandazi *417 Army Equity Fund Hospital of Athens, Greece Background & objectives: Synovial sarcoma is a rare malignant soft tissue tumour of unknown histologic origin usually affecting the extremities, can also involve mediastinum and viscera. Synovial sar- coma can occur in any age. More than half of patients are teenagers and young adults. Methods: A 25 year old female patient with a history of known synovial sarcoma involving the kidney presented to our hospital with symptoms of abdominal pain and hypoalbuminemia. Imaging diagnosis revealed a mass occupying the retroperitoneal space and extending to the diaphragm. Upon surgical resection, the mass weighing of 2365 gr and 30x20x5,5 in dimensions, having a soft and gelatinous consistency, Results: Microscopic examination revealed a biphasic tumour of mes- enchymal origin with an epithelial and a spindle cell component in varying proportions. The epithelial component was consisted of cystic areas lined by epithelial cells and the sarcomatous component was composed primarily of monotonous, relatively small spindle cells arranged in dense or vague fascicles, showing severe nuclear atypia and high mitotic activity (15 mitosis/10 HPFs).Few areas exhibiting hypercellularity whereas areas of necrosis were present in the poor differentiated part of the tumour. Mast cells were abundant. Immu- nohistochemistry showed strong positivity of tumour cells for TLE-1, Bcl-2,EMA and CD99 while cells of the epithelial component were positive for AE1/AE3 and Cam5.2 Conclusion: Biphasic synovial sarcoma has a variable prognosis. Favourable and unfavourable histological features are described pre- cisely. Most distant recurrences occur within a few year but late recur- rences can develod as well. Poorly differentiated tumours show aggres- sive behaviour with metastasis most commonly in lung and bones. In our case, the initial diagnosis of synovial sarcoma was made in 2011 with a late recurrence and the involvement of the right mediastinum by 2017.By 2018, our patient showed distant metastases with a poor outcome. E-PS-22-006 Clinicopathologic spectrum of myxoid tumours: a diagnostic chal- lenge and helpful ancillary studies Y. Belogrivtseva*, A. Tushir, K. Khouri, D. Proca *Temple University Hospital, USA Background & objectives: Myxoid tumours of the soft tissue show significant variability in their biological behaviour. They include benign tumours, ones that tend to recur locally, and malignant tumours. Broad morphological overlap within this group presents diagnostic difficulties for the pathologist.