ECP 2022 Abstract Book

Virchows Archiv (2022) 481 (Suppl 1):S1–S364 13 mesenchymal tumours including liposarcoma, extraskeletal myxoid chondroscarcoma and myoepit helial tumours. Understanding its pseudosarcomatous histological features and appropriate clinico-radiological correlation is key to avoiding this diagnostic pitfall. Methods: We describe the morphological features of a rare, extensively cystic chondroid lipoma occurring in the trunk of an adult female on frozen and paraffin sections. In addition, we performed molecular analysis using anchored multiplex PCR assay (Archer FusionPlex® Sarcoma Panel) for gene fusion detection. Results: Incisional biopsy submitted for frozen section inter pret ation showed sheets and cords of large, round to epit helioid tumour cells wit h vacuolated cytoplasm and nuclear atypia, initially wor risome for an aggressive tumour. The presence of lipoblasts, myxohyaline matr ix a n d ma t u r e a d i p o c y t e s we r e b e t t e r a p p r e c i a t e d o n subsequent paraffin sections. Gene fusion analysis revealed the presence of a C11or f95 (exon 5) – MKL2 (exon 12) gene rearrangement, further supporting the diagnosis of a chondroid lipoma. Conclusion: Frozen section evaluation of chondroid lipomas present diagnostic challenges. Detection of MKL2 gene fusion is helpful in distinguishing this rare pseudosarcomatous entity from its morphologic differentials and in guiding appropriate patient management. E-PS-22-011 Post-denosumab morphological and immunohistochemical findings in giant cell tumour of bone – is there a risk for malignancy? A. Cohn*, D.M. Pop *Emergency University Hospital, Bucharest, Romania Background & objectives: Giant cell tumour of bone (GCT) is an intermediate and locally aggressive neoplasm. This study aims to emphasize the morphological and immunohistochemical features in a GCT treated with denosumab for 12 months and to assess the risk of malignant transformation. Methods: We present the case of a 22-year-old female, admitted to “Foisor” Orthopedics Hospital for pain in the left knee. Imaging examination revealed a lytic lesion with benign features expanding the proximal epiphysis of the left fibula and a biopsy was taken. The histopathologic aspects were those of a giant cell tumour of bone associated with a secondary aneurysmal bone component. Results: Covid-19 restrictions in the hospital led to prolonged neo- adjuvant treatment with denosumab (15 doses). After one year of therapy, en-bloc resection of the proximal fibula was performed. Grossly, the tumour was well-defined and measured 6.5/4/2.5 cm. Extensive microscopic examination of the surgical specimen showed complete disappearance of the osteoclastic component, new bone formation, and a densely cellular stromal-like proliferation of spindle cells with osteoid deposition. The tumour was completely circumscribed by new bone formation. The neoplastic stromal-like cells were positive for MDM2 immunohistochemical stain. The correlation between the histopathologic features and immunohisto- chemical results made us conclude that a low-grade osteosarcoma has developed under the long-term treatment with denosumab. Conclusion: Malignant transformation occurring in denosumab- treated GCT of bone has rarely been reported. In our case, the osteosarcoma-like features observed on the surgical specimen and the MDM2 immunohistochemical positivity confirmed the malignancy. Therefore, close follow-up was recommended. This case report is consistent with observations made by other authors who have definitively found malignant transformation after long- term treatment with denosumab in GCT. E-PS-22-012 Hemosiderotic fibrolipomatous tumour - a potential diagnostic pitfall A. Dumitru*, M. Sajin, M. Costache, B. Cre ț u, C. Cîrstoiu *Carol Davila University of Medicine, Romania Background & objectives: Hemosiderotic fibrolipomatous tumour is an locally aggressive uncommon soft tissue neoplasm which com- monly occurs in the ankle and foot. Morphologic data suggests that hemosiderotic fibrolipomatous tumour is related to yet another rare, locally aggressive tumour: pleomorphic hyalinizing angiectatic tumour. Methods: A 61-year-old man was referred to the Department of Orthopaedics and Traumatology of the University Emergency Hos- pital in Bucharest for a volumetric increase of a left foot mass which in recent months had begun to cause functional discom- fort. After thorough investigation it was decided to opt for surgical option. The surgical sample was sent the Pathology Department for histopathological assessment. Results: Microscopically, the lesion was composted of clusters of variably sized, thick walled blood vessels surrounded by a thick rim hyalin. The tumour cells were arranged in poorly defined fascicles with abudent brown pigment (hemosiderin), and nuclear pseudo inclusions. At the periphery, the lesion showed a pseudo infiltrative pattern of growth. There were not cytological atypia and mitotic figures but bizarre-looking tumour cells and rare multinucleated cells have been observed. From the immunohistochemical point of view, we found that the lesion was strongly and diffusely positive for CD34, while it was negative for SOX10, Calretinin and S-100. Few tumour cells were calponin positive. The proliferation index (evalued by KI67) was <3%. Conclusion: To conclude, though rare, it is important for the histopathologists to be aware and recognize this unusual entity and distinguish it from other pigmented spindle cell lesions. Long term follow-up is recommended as rare cases of malignant transformations were reported. E-PS-22-013 Cervico-thoracic lipoblastoma of the adult: a case report of a rare entity J. Fernandez-Perez*, J.A. Ruiz-Maciá, A. Caballero-Illanes, A. Garzón-Arana, M. Segado-Martínez, J. Bejar-Valera, L. Sánchez-Godoy *Hospital Universitario “Virgen de la Arrixaca”, Spain Background & objectives: Lipoblastoma is a rare benign neoplasm predominantly diagnosed during infancy. It can remain asymptomatic for years and be a casual finding in the adult, causing diagnostic pitfalls. We present a case of an adult lipoblastoma with an unusual presentation. Methods: A 34 year-old male presented with a neck and upper thorax mass. Ultrasound examination revealed a solid heterogeneous tumour. The specimen was a well-defined encapsulated nodule. Cut surface was solid, lobulated, yellow- white and myxoid. Tumour consisted of adipocytes in different stages of maturation, with atypia, lipoblasts and branching vessels. Stroma was myxoid. Neoplastic cells were CD34+, p16+ and MDM2-. Results: Lipoblastoma is a benign neoplasm of embryonal white fat predominantly localized in the trunk and the extremities. In S338