ECP 2023 Abstracts

S359 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 all cases. Five cases were consistent with conventional CSR grade I in three cases and grade II in two cases. In a case the diagnosis of dedif- ferentiated CSR was made. This patient underwent chemoradiotherapy, but he died 2 years later. Five patients have no recurrence. Conclusion: Conventional chondrosarcoma is the most common vari- ant of CSR. Histologic grading is challenging and is subject to high rates of interobserver variability. Tumour grades are predictor for local recurrence, systemic metastasis, and survival. The decision of whether to perform reconstruction is based on lesion location and defect size. Access to chest wall reconstruction forms a barrier to patient compli- ance. The prognosis of chondrosarcoma varies widely and is based on tumour grade, stage and subtype. E-PS-22-026 Activation of PIK3/mTOR pathway in a case of spindle cell ada- mantinoma with dedifferentiation S. Mangray*, S. Chen, T. Scharschmidt, A. Shenoy, B. Setty, L. Bieder- man, M. Conces, V. Prasad, C. Cottrell *Nationwide Children’s Hospital, USA Background & objectives: There is limited data on the comprehensive genomic profile (CGP) of spindle cell adamantinoma (SpAda). Herein we report the CGP in a SpAda with focal dedifferentiation arising in the soft tissue and tibia of an 18-year-old young man. Methods: The morphologic and immunohistochemical features of the tumour are reviewed. The genomic workup performed on a paired ger- mline (blood sample) and snap-frozen tumour, and included germline and somatic variants, copy number (CN) variations, structural varia- tion (SV), DNA methylation (DNAmet) sarcoma classification, and transcriptomic outlier (TO) analyses. Results: The resected 2.7 x 1.6 tumour was centred in the soft tissue but focally involved the tibial cortex and medulla. Histologically, there was a cellular spindle cell proliferation in short fascicles with focal pleomorphic cells. The peak mitotic rate was 30/10 HPFs and focal necrosis was noted. No epithelial component was present. The tumour was diffusely positive with pan keratin and p63, while S-100, CD99, EMA, desmin, and NKX2.2 were negative. Genomic profiling revealed: NF2 somatic alteration [NM_000268.3 (NF2) :c.14 6dupT:p.Leu 49fs]; hyperdiploidy; enhanced oncogene expression (MET Log2 fold change 6.1, PIK3R1 4.8, and EGFR 4.8) by TO analysis; chromosome 22 copy number loss (NF2); DNAmet score of 0.3 (no match); and no SV. Conclusion: The morphologic features, immunohistochemical pro- file, and CGP are consistent with a SpAda with focal dedifferentia- tion. The CGP demonstrated overexpression of MET, EGFR, and PIK3R1 in this tumour suggesting activation of the PI3K/mTOR signalling pathway through multiple receptor tyrosine kinases. Although the standard management for recurrent disease in adaman- tinomas is surgery, the genomic findings described suggest a potential role for the use of tyrosine kinase inhibitors should there be advanced progression of disease. E-PS-22-027 Case report: uncommon case of epithelioid angiosarcoma post endovascular aortic repair I. Mergeanu*, A. Birceanu, A. Procop *University Emergency Hospital Bucharest, Poundbury Cancer Insti- tute, Romania Background & objectives: Epithelioid angiosarcoma is a rare entity, moreover so when it arises post endovascular aortic repair, following descending aortic aneurysm. The latest literature reviews cite no more than 15 cases reported up to date of such occurrences. Methods: Our Department of Pathology received a biopsy specimen from a pelvic mass which had been fixed with 10% buffered formalin and processed by conventional histopathological methods, using par- affin embedding, sectioning and Haematoxylin–Eosin (HE) staining. Afterwards, the sections were deparaffinized and prepared for immuno- histochemical staining, using the following markers: AE1/AE3, S100, desmin, SATB2, CD99, SS18-SSX, CD31, NKX2.2, ERG and FLI1. Results: We report the case of a 68-year-old female patient with previ- ous history of descending aorta aneurysm, that had undergone endovas- cular aortic repair with a synthetic graft. Three years later, the patient presented with pelvic mass extending towards the right thigh, invading the quadriceps and the femur. The biopsy revealed sheets of malignant, pleomorphic, epithelioid cells, focally exhibiting vasoformative pat- tern. Immunohistochemical studies showed that the tumour cells were AE1/AE3 (-), S100 (-), desmin (-), SATB2 (-), CD99 (+), CD31 (+), SS18-SSX (-), NKX2.2 (-), ERG (+) and FLI1 (+), therefore confirm- ing the diagnosis of post-EVAR epithelioid angiosarcoma. Conclusion: Epithelioid angiosarcomas are highly aggressive malig- nant entities with rapid evolution. According to literature, the period of time from the procedure and until the appearance of the tumour is relatively short. This warrants a very prompt diagnosis, in order to ensure maximum chances in overall survival, but more often than not this proves to be a tall order. The spectrum of differential diagnoses is wide; therefore, an accurate past medical history is of paramount importance to enunciate a diagnostic algorithm. E-PS-22-028 Osteosarcoma arising from an osteochondroma in a patient with multiple hereditary exostoses L.D. Micoogullari*, A. Avci, E. Ozmen *Izmir Katip Celebi University, Ataturk Training and Research Hospi- tal, Department of Pathology, Turkey Background & objectives: Multiple hereditary exostoses (MHE) is an autosomal dominant skeletal disorder with a rare incidence. MHE presents with painless and slow-growing multiple osteochondromas. In this case, we report an osteosarcoma arising from an osteochondroma in a 28-year-old male patient with MHE. Methods: A spinal mass specimen from L3 vertebrae consisting of multiple nodular pieces of bony tissue, measuring in total of 17x15x3 cm, was decalcified and then sampled. Paraffin-embedded tissue sections of this specimen were evaluated for the histopatho- logical characteristics. Demographic, clinical, and imaging data were collected. Results: A 28-year-old male patient admitted to our hospital with the complaint of back pain and loss of sensation in the lower extremities. His examination showed multiple bony exostoses throughout his body. He mentioned that he has MHE syndrome. He noticed that the lesion in his lumbar region has rapidly grown. Computed tomography revealed a mass with 10 cm thickness at the level of L3 vertebrae. Histopathologi- cal examination revealed a characteristic fibrous cartilaginous cap cov- ering a lace-like osteoid tumour with irregular trabeculae. Tumour cells showed marked nuclear atypia, pleomorphism and frequent mitoses including atypical mitoses. Diagnosis of “osteosarcoma arising from an osteochondroma” was made. Conclusion: MHE, also known as diaphyseal aclasis or familial osteo- chondromatosis, has heterogenous genetical characteristics which are shown to be depending on two genes: exostosin-1 (EXT-1) gene located at 8q24 and exostosin-2 (EXT-2) gene located at 11p11–p12. Malignant transformation of osteochondromas is a rare entity to encounter. When malignant transformation occurs, the majority of cases show transfor- mation to chondrosarcomas. In English-language literature, apart from our case, there are only 13 cases that report malignant transformation of MHE to osteosarcoma.