ECP 2023 Abstracts

S362 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 location of the tumour in the third case permitted an earlier diagnosis despite the absence of biochemical alterations. E-PS-22-036 Infantile fibrosarcoma with ETV6-NTRK3 fusion: a rare case report O. Sahin*, I. Tosun, G. Unverengil, I.E. Zemheri *University of Health Sciences, Umraniye Training and Research Hos- pital, Department of Pathology, Turkey Background & objectives: Infantile fibrosarcoma (IFS) is a rare malignant fibroblastic tumour that typically presents in the first 1 year of life. ETV6-NTRK3 fusion is present in the majority of cases. IFS is a locally aggressive tumour; recurrence and metastasis are rarely seen. Methods: We present a case of 3 months old baby girl with a rap- idly enlarging right axillary mass. On clinical examination, contrast- enhanced magnetic resonance imaging (MRI) revealed a 36x26 mm densely contrasted solid mass lesion in the posteromedial aspect of the proximal humerus. Tru-cut biopsy was performed, followed by total excision. Results: Tru-cut biopsy revealed a tumoral lesion consisting of spin- dle cells arranged in crossed fibres. There were haemorrhages, but no necrosis. The mitotic activity was 8/mm2. Immunohistochemically, negative immunostaining for S100, CD34, Desmin, Myogenin, and MyoD1 was observed. Ki67 proliferation index was 80%. The tru-cut biopsy is diagnosed as “malignant spindle cell mesenchymal tumour.” In the excised specimen, a partially encapsulated nodular mass with a firm consistency was observed on gross examination. Microscopi- cally, the neoplasm was highly cellular and was composed of spindled to immature-round cells. Necrosis and calcification were observed. Mitotic activity was 14/mm2. Molecular analysis revealed ETV6- NTRK3 fusion-positivity. Conclusion: Infantile fibrosarcoma is a rare neoplasm resembling other paediatric mesenchymal neoplasms. Despite having features similar to those of adult fibrosarcoma, IFS is a completely different entity with better clinical outcomes and molecular features. In most cases, ETV6- NTRK3 fusion is detected as a result of chromosomal translocation, t(12:15). This translocation has also been detected in cellular congeni- tal mesoblastic nephroma and secretory carcinomas of the breast and salivary glands. Histomorphologic findings and clinical history will help reach the correct diagnosis. E-PS-22-038 Endometriosis of sciatic nerve: case report L. Simic*, J. Jevtic, G. Djuricic, M. Popovic Vukovic, J. Sopta *Institute of Pathology, Serbia Background & objectives: Endometriosis is defined as the occurrence of endometriotic tissue outside the uterus. The most affected areas are the pelvic peritoneum, ovaries, and recto-vaginal septum. Nearly 5–10% of women in their reproductive years develop endometriosis. Methods: We present a case of a 26 years old women, which was examined because the continuous back and leg pain with severe exac- erbation before and during menstruation. MRI showed diffuse thick- ness of left sciatic nerve with focally presented cystic formation. They decided to do biopsy. Results: Grossly tissue were fragmented, soft, greyish to reddish with small pseudocystic structures. Microscopically, on H&E examina- tion among fields of fibrous and neural tissue, there were parts with glandular formations lined by columnar epithelium, surrounded with hypercellular stromal layer which resemble endometrial stroma. Immu- nohistochemical analyses (CK AE1/AE3+, CK7+ in glands, CD10+, PAX8+ in stroma, Oestrogen+, Progesterone+ in both glands and stroma) correlated with morphological characteristics proved diag- nosis of sciatic nerve endometriosis. In addition, patient mentioned confirmed cystic formation on her last gynaecological US examination, but since now she has never been diagnosed endometriosis. Conclusion: Endometriosis rarely involves major nerves, so affection of sciatic nerve is very rare condition. Mostly it is caused by direct extension of deeply infiltrative recto-vaginal disease, but in a minority of cases it can be isolated form, without any apparent signs of pelvic endometriosis. Since severe clinical presentation, and possible destruc- tion of the nerve, endometriosis of sciatic nerve must be always consid- ered when it comes to possible cause of unexplained pelvic nerve pain. E-PS-22-039 Rhabdomyosarcoma in the oral cavity of a paediatric patient: a rare case B. Simsek*, E. Atik Doğan, D. Gürsoy Kuzuluk, M. Cemaloğlu *Hatay Mustafa Kemal University, Turkey Background & objectives: Rhabdomyosarcoma(RMS) is a rare,rapidly growing,aggressive malignant neoplasm mainly affecting children and adolescents. We present a case of rhabdomyosarcoma detected in the hard palate of a 6-year-old boy who presented to the clinic with a complaint of swelling on the cheek. Methods: 3 punch biopsy materials taken from the hard palate were sent to our pathology laboratory with clinical prediagnoses of sar- coma, acinic cell carcinoma and maxillary sinus tumour. In the light of histopathological findings Small Round Cell Tumours, Neuroendo- crine Tumour, Plasma Cell Neoplasia and Malignant Melanoma were included in the differential diagnosis. A large immunohistochemical panel covering all differential diagnoses was applied. Results: Histopathological examination showed a tumoral lesion formed by cells with narrow eosinophilic cytoplasm, hyperchromatic round-oval nuclei, arranged in the form of islands and cords with crush artifact in the fibrocollagenized stroma with occasional myxoid changes. Cells with eccentric or spindle nuclei were also noted infre- quently. No rosette formation was observed. Immunohistochemical examination revealed that the tumour cells were positive for myogenin, desmin and vimentin. The Ki67 proliferation index was ~80-90% per HPF. As a result of the histopathological and immunohistochemical exami- nation, the patient was diagnosed with embryonal RMS. There is no paediatric oncology unit in our hospital, so the patient was referred to another centre for oncological evaluation and treatment. Conclusion: The patient was classified as intermediate risk group according to the Europen paediatric Soft tissue sarcoma Study Group (EpSSG) in the referred centre. Embryonal RMS has being treated via vincristine, actinomycin D, cyclophosphamide and irinotecan. A pathological diagnosis for RMS is necessary because a specific diag- nosis cannot be made based on clinical findings alone. In conclusion, the current case was found worth presenting as a rare diagnosis in the literature. E-PS-22-040 Secondary malignancy in Li-Fraumeni syndrome patient J. Tuziak*, P. Wiśniewski, H. Koseła-Paterczyk, P. Rutkowski, K. Seliga, A. Tysarowski, A. Szumera-Ciećkiewicz *Maria Sklodowska-Curie National Research Institute of Oncology Warsaw, Poland Background & objectives: Li-Fraumeni syndrome (LFS) is a rare, autosomal dominant genetic disease with high penetrance characterised by germline TP53 mutations. Females with LFS and before age 30 have a nearly 90% and 25% lifetime risk of developing breast cancer and sarcoma, respectively. Methods: A 29-year-old female was admitted for consultation on a chest tumour. Five years earlier, she was diagnosed with breast can- cer (luminal type, pT4b N(sn)1a) and underwent mastectomy with