ECP 2022 Abstract Book

Virchows Archiv (2022) 481 (Suppl 1):S1–S364 13 our case, lipoblastoma was found in the anterior neck and into the upper thorax. Grossly, cut surface is soft, lobulated, yellow-white and can show myxoid areas, cystic spaces or well-delimited fat nodules. Histo- logically, lipoblastoma consists of lobules of adipocytes in vari- ous stages of maturation. Adipocytes are positive for CD34 and S100 whereas mesenchymal cells stain for desmin. These cells are separated by fibrous septa and plexiform vessels. Several genetic alterations have been described. Molecular analysis didn’t demon- strate PLAG gene rearrangement, but this is not mandatory for the diagnosis of lipoblastoma. Conclusion: Lipoblastoma is a benign neoplasm of embryonal white fat of which rare cases have been reported in adults. Lipoblastoma can cause diagnostic pitfalls with other adipocytic neoplasms (particulary myxoid liposarcoma), requiring molecular studies for diagnostic confirmation. Detection of molecular alterations such as PLAG gene rearrangement are desirable but not mandatory. Prognosis after excision is excellent, with no risk of metastasization and low rates of recurrence after complete excision. E-PS-22-014 Epithelioid Hemangioendothelioma: a case series of a rare vas- cular neoplasm S. Frini*, O. Belkacem, L. Belaid, S. Ben Cheikh, S. Mestiri, A. Bdioui, H. Hamchi, S. Hmissa *Pathology Department, Sahloul University Hospital of Sousse, Tunisia Background & objectives: Epithelioid Hemangioendothelioma (EHE) is an extremely rare malignant proliferation, accounting for <1% of all the vascular tumours. It’s locally-aggressive, affecting one or multiple organs (such as soft tissues, lung, liver and bones). Herein, we aim to describe its clinico-pathological features. Methods: All cases of EHE diagnosed during a 24 year-period (1997-2021) and compiled by the Cancer Registry of the Center of Tunisia, which provided clinical data and pathological reports. 4 cases were included in our study. Results: Three patients were male and one was a female. Patients’ age ranged from 38 to 67 years (mean age 47). The female patient had Von Recklinghausen disease. Two tumours , identified by imaging studies , developed in the vertebral bones, one in the lung and one in soft tissue of the thumb. Histologically, they displayed strands, cords and solid nests of epithelioid cells with vacuolated cytoplasm and mild nuclear atypia, set in a myxo-hyaline stroma . In 2 cases, nuclei showed promiment nucleoli, marked atypia and high mitotic-rate. The lung EHE displayed micro-calcifications and focal necrosis. In Immunochemistry, tumour cells expressed CD34 in all cases and ERG in one case. Conclusion: EHE is a rare aggressive tumour, with unknown pathogenesis, that is often misdiagnosed because of its atypical presentation and morphological similarities with other epithelioid vascular neoplasms, such as haemangiomas and angiosarcomas. When available, the molecular profile of these tumours should be explored as almost all EHEs harbour WWTR1-CAMTA1 or YAP1- TFE3 fusions; and identifying these alterations may, in the future, benefit the patients with immunotherapy and selective inhibitors treatments. E-PS-22-015 Giant cell tumour of the bone under treatment with Denosumab J. Gama*, J. Madeira, R. Oliveira, C. Faria, V. Almeida, F. Ramalhosa, B. Sepodes, G. Fontinha, C. Courelas, A. Alves, M.A. Cipriano *Centro Hospitalar e Universitário, Portugal Background & objectives: Giant cell tumour (GCT) of the bone is a locally aggressive and rarely metastasizing neoplasm. Some cases may be treated with denosumab and may exhibit important histologi- cal changes. Our goal was to characterize the histology of GCT after denosumab treatment. Methods: A retrospective study included 5 patients submitted to neoadjuvant treatment with denosumab between 2019 and 2022 and subsequent surgical resection. Clinical and pathological parameters, including the duration of treatment, gender, age at diagnosis, location, histologic descrip- tion and percentage of tumour response were recorded. Results: According to location, tumour developed in the radius (in two), fibula (1), vertebral column (1) and acetabulum (1). The median duration of the treatment was 7 months (4-9 months). Tumour response was complete in four, and in one, up to 40% of tumour was viable. After a median follow-up of 5 months (1-22 months) one patient relapsed, 7 months after surgery. Histologically, there was replacement of the tumour by woven bone and fibrous tissue was found between the trabeculae. There was a general decrease in the number of giant cells, which were absent in four patients. In one the histological appearance mimetized an osteosarcoma. Conclusion: Denosumab inhibits RANKL and thus reduces bone lysis, which helps control the disease. This drug induces morphological changes in bone histology that ought to be recognized in order to make the differential diagnosis with its mimics, which include malignant lesions. E-PS-22-016 Lipoma arborescens of the knee: report of a rare case S. Graja*, M. Mellouli, O. Boudawara, M. Triki, C. Chaari, N. Gouiaa, T. Boudawara, R. Kallel *Department of Pathology, Habib Bourguiba University Hospital, Sfax, Tunisia Background & objectives: Lipoma arborescens (LA) is a relatively unusual benign intra-articular lesion, with only few cases reported in the literature. The knee is the most commonly involved joint. The aim of the study is to discuss clinicopathological features of this rare disease. Methods: An 80-year-old Women was presented to the depart- ment of orthopaedic surgery with gradually increasing pain and swelling in the left knee. Results: On examination, there was a diffuse swelling of the left knee, which was doughy in consistency with limited range of movements. There was no history of trauma. An arthrotomy was performed with a total synovectomy and resection of hypertrophic multilobulated synovial tissue. The histological examination revealed hypertrophic villous projections of fat lined by synovial cells with variable scattered inflammatory cells. The postoperative period was uneventful and the patient had good range of movements over left knee without recurrence in 3 months of follow up period. Conclusion: LA is a lipomatous proliferation of subsynovial con- nective tissue often associated with chronic joint disease. It affects typically adults aged in fourth and fifth decades of life. It commonly involves the knee. The aetiology remains unclear. Recent work has shown that this adipocytic proliferation lacks HMGA2 overexpres- sion. Recurrence is uncommon. LA should always be considered S339