ECP 2023 Abstracts

S363 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 chemotherapy and radiotherapy. The patient remained without recur- rence or progression until the tumour mass of soft tissues in the post- radiotherapy field was identified. Results: The biopsy material revealed epithelioid cells, with high cytological atypia and mitotic activity (26 mitoses/10HPF), with- out necrosis. The immunohistochemical profile of neoplastic cells showed: Vimentin(+), EMA(-/+), CD34(-/+), ERG(-), CKAE1/ AE3(-), ER(-), PGR(-), HER2(-), GATA3(-), PAX8(-), S100(-), SOX10(-), HMB45(-), SMA(-), Desmin(-), LCA/CD45(-), CD30(- ), INI1(+), CD163(-). The molecular analysis with the NGS extended sarcoma panel (53 gene fusions and 14 gene mutations) was negative. We compared the primary breast cancer image with the current neoplasm and excluded recurrence; the undifferentiated sarcoma high-grade, G3 as a second malignancy was diagnosed. Additionally, the genetic predisposition test (blood) revealed a TP53 germline mutation. Conclusion: Breast cancer in young women should trigger test- ing its association with the inheritance of a pathogenic variant in one of the breast cancer susceptibility genes. The LFS patients require special care i.e., favouring the mastectomy rather than lumpectomy to avoid adjuvant radiotherapy and subsequent risk of radiation-induced second primary malignancies, dose-adjusted careful consideration of radiation when indicated post-mastectomy. The diagnostic challenge includes differential diagnosis between breast cancer and sarcoma, possibly secondary and/or radiotherapy- induced malignancies. E-PS-22-041 Myxoid angiomatoid fibrous histiocytoma with EWSR1-CREM fusion: a case report J. Tuziak*, M. Wągrodzki *Maria Sklodowska-Curie National Research Institute of Oncology Warsaw, Poland Background & objectives: Angiomatoid fibrous histiocytoma (AFH) is a rare mesenchymal tumour. It harbours EWSR1-CREB1 or EWSR1- ATF1 gene fusion. Hereby we present the first case of myxoid AFH of soft tissue with CREM fusion. Methods: A 56-year old woman presented with a mass located between her left humerus and clavicle. The tumour was evaluated on MRI. First a fine needle biopsy then resection of the mass after neoadju- vant therapy was conducted. Tumour was assessed using extensive immunohistochemistry panel and molecular studies - Next Generation Sequencing (NGS). Results: Gross sectioning revealed tan, solid soft tissue tumour with bloody spaces, measuring 4,8 x 5,8 x 4,5 cm with destruction of the clavicle. On H&E slides there was a lobulated neoplasm with epithelioid, dys- cohesive cells exhibiting eosinophilic cytoplasm with nuclear pseu- doinclusions. The presence of multinucleated giant cells was also noted. Part of the tumour showed nested architecture. Tumour stroma was predominantly chondro-myxoid. The neoplastic cells exhibited: membranous CD99 (MIC2), and retained INI1 (MRQ27) nuclear stain- ing with focal EMA (E29) and podoplanin (D2-40) expression. NGS CREM[3]-EWSR1[13] fusion was detected. Conclusion: Our tumour shows striking resemblance to previously described intracranial myxoid AFH-like tumour occurring in central nervous system. To the best of our knowledge, it is the first tumour with this rear- rangement in soft tissue. Since CREM gene belongs to the CREB fam- ily transcriptor factors along with ATF1 and regarding the presence of EWSR1-CREM fusion in classic AFH, the myxoid tumours with EWSR1-CREM fusion should be regarded as myxoid variant of AFH both in central nervous system and in soft tissues. E-PS-22-042 Giant dedifferentiated liposarcoma of the omentum with rhabdo- myosarcomatous differentiation - a rare case C. Valavanis*, E. Souka, G. Stanc *Molecular Pathology Unit Metaxa Cancer Hospital, Greece Background & objectives: Liposarcoma is the most common soft tissue sarcoma and accounts ≈20% of all mesenchymal malignancies. Primary tumours of the omentum are very rare. The incidence is not known, and the information is available in the literature only from case reports. Methods: A 55-year-old man presented with abdominal pain, nau- sea, weight loss and gastric haemorrhage. CTscan showed a large mass 19X16X12cm in dimensions, which causes pressure to the stomach from outside, in touch with the liver, gallbladder, anterior surface of the stomach and duodenum. Partial gastrectomy for duodenal ulcer has been performed in 1993. A distal partial gastrectomy and omentomy was made. Results: Microscopic examination revealed morphology of well dif- ferentiated liposarcoma. The neoplasm was characterised by cells with high-grade atypia, focally by the presence of multinuclear bizarre cells or signet-ring lipoblasts. Foci of pleomorphic liposar- coma and rhabdomyosarcomatous differentiation were present. The mitotic activity was high, 23mitoses/10HPF. Cystic degeneration of the tumour and necrosis were seen. Immunochemistry showed positivity for S-100, CD34, CDK4, MDM2, SMA, Desmin and Vimentin. Negative were CD117, HMB45, Melan A, CK7, CK19, CK8/18, CK20, MUC2 and MUC5AC. The diagnosis of high-grade dedifferentiated liposarcoma with pleo- morphic component and rhabdomyosarcomatous differentiation was made. Conclusion: The main therapy for omental liposarcoma is surgical removal. The type of gastrectomy depends on the location of the tumour. Lymph node dissection may be unnecessary. Clear guidelines for chemotherapy and radiotherapy in patients with omental liposarcoma does not exist in the literature. In high-grade liposarcomas, adjuvant therapy may be considered because of a high local recurrence rate (70-90%). E-PS-22-043 Dedifferentiated leiomyosarcoma with heterologous osteosarcoma component in the thigh: case report and review of literature M. Zaryouhi*, R. Ben Tayab, L. Chbani *Hassan II hospital University, Morocco Background & objectives: The terminology dedifferentiated leiomyo- sarcoma refers to a tumour characterized morphologically by an abrupt transition from a classical leiomyosarcoma to a high-grade sarcoma, not expressing muscle markers. The aim of this report is to explain the histological features of dedif- ferentiated leiomyosarcoma. Methods: We are reporting a case of 43-year-old woman who, after three surgeries, chemotherapy, and radiation therapy on a previously diagnosed pleomorphic leiomyosarcoma grade 3 of the French Federa- tion of Comprehensive Cancer Centers (FNCLCC) grading system, had a local recurrence made of a subcutaneous permeation nodule on the posterior compartment of the left thigh. Results: Histomorphologic features of this nodule revealed a bipha- sic pattern. The first one is made of atypical spindle cells arranged in short fascicles, focally pleomorphic with an ovoid hyperchro- matic nucleus and eosinophilic cytoplasm typical of a leiomyosar- coma. The second component has a distinctive osteoid laid down by malignant cells.