ECP 2023 Abstracts

S358 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 E-PS-22-022 CD16 (FcRIII) expression might play a pivotal role in neurofi- broma progression as a tumour-associated immune cell K. Kim*, M. Yeo, K. Suh, D. Kang, J.E. Choi *Chungnam National University, Republic of Korea Background & objectives: Neurofibroma (NF) is a benign tumour in the peripheral nervous system, but it can infiltrate around structures and cause functional impairment and disfigurement. We hypothesized that inflammation is relevant to tumour progression with infiltrative growth in NF. Methods: We evaluated the expressions of CD16, CD68, and SOX-10 in the 45 cases of neurogenic tumours (neurofibromas (NFs), n=24; atypical NFs, n=6; atypical neurofibromatous neoplasms of uncertain biologic potential (ANNUBP), n=9; malignant peripheral nerve sheath tumour (MPNST), n=3; neuroma, n=3). Results: CD16 expression increases along with CD68 positivity in the tumour microenvironment (TME) of the atypical NFs and ANNUBPs. In the atypical NFs and ANNUBPs, CD16 increased more than in the NFs (P=0.006 and P=0.005, respectively), in contrast to deplet- ing CD16 expression in the MNPSTs than ANNUBPs (P=0.002). The quantitative variables were compared using the Kruskal-Wallis H test and Benferroni Correction Method. Conclusion: Increased expression of CD16 was detected in the NFs but decreased with malignant progression. The CD16 overexpression with CD68 positivity in the atypical NFs and ANNUBPs potentially reflects that the TME immune modulation could be associated with the NF progression. Further studies should be explored therapeutic approaches for targeting the mechanism of CD16 associated with an immunomodulatory role in accelerating NF growth. E-PS-22-023 Intramuscular nodular fasciitis with MYH9-USP6 fusion: a case report B. Konuk*, I. Tosun *University of Health Sciences, Umraniye Training and Research Hos- pital, Department of Pathology, Turkey Background & objectives: Nodular fasciitis is a benign myofibroblas- tic neoplasm. it is mostly located in the upper extremity, head/neck, trunk. About 20 percent of cases have a history of trauma. It can be confused with malignant mesenchymal tumours due to rapid divisions and various morphological features. Methods: A 50 year old male patient presented with a painful mass at the level of the 8th rib on the right. After the evaluation, the mass was excised together with the attached rib. Macroscopically, a firm beige lesion with irregular borders was seen invading the muscle. Surgical margins were intact. Results: In microscopic examination, the tumour was composed of short, intersecting fascicles of myofibroblastic cells in a loose myxoid matrix. Presence of mixed inflammatory infiltrate tissue culture appear- ance and frequently extravasated erythrocytes were remarkable. No significant cellular atypia, atypical mitosis, or necrosis were observed. Fibroblastic benign and malignant neoplasms such as nodular fasciitis, fibromatosis, benign fibrous histiocytoma, infantile fibrosarcoma, fibro- myxoid sarcoma, dermatofibrosarcoma protuberans were considered in the differential diagnosis. Sma positive, cd34,s100 negative, desmin focal positive was evaluated in immunohistochemical studies. Fusion between MYH9 gene exon 1 and USP6 gene exon 6 was detected by NGS method. This supported the diagnosis of nodular fasciitis. No recurrence was observed in the 1-year follow-up. Conclusion: Nodular fasciitis is considered as reactive lesion due to its self-limiting nature, post-traumatic formation and non-recurrency. However, recent studies have identified the USP6 mutation, reveal- ing that nodular fasciitis represents a clonal neoplastic proliferation. Hence, it can mimic malignant mesenchymal tumours, It is important to rule out other differential diagnosis and avoid over-treatment. We aimed to present our case because of its infrequent intramuscular locali- zation within a case with no history of trauma. Also, MYH9:USP6 fusion which supports the diagnosis, detected in this case by using NGS analysis. E-PS-22-024 Primary epithelioid rhabdomyosarocma of gastrointestinal tract O. Kuczkiewicz-Siemion*, M. Lenarcik, M. Wągrodzki, B. Gierej, A. Mróz, A. Szumera-Ciećkiewicz *Department of Pathology, Maria Sklodowska-Curie National Research Institute of Oncology Warsaw, Poland Background & objectives: Rhabdomyosarcomas are classified accord- ing to WHO 2020 into embryonal, alveolar, pleomorphic and spindle cell/sclerosing types. Recently a morphologically exceptional variant called “epithelioid RMS” was identified. Here we present a case report of primary epithelioid RMS of gastrointestinal tract. Methods: A 69-year-old female was admitted for consultation on a tumour 5.3 cm in diameter located in the proximal jejunum; the perfo- ration and ulceration of the intestinal wall were described. The patient was previously treated for metastatic lung squamous cell carcinoma. Results: In the initial evaluation of the biopsy material, lymphoma suspicion was described. Microscopically, the tumour was composed of a solid infiltrate of poorly differentiated, small cells with high mitotic activity (12 mitoses/10HPF), no necrosis, with numerous lymphoid cells in the background. The immunohistochemical analysis showed: Desmin(+), Myogenin(+/-) in scattered cells, MyoD1(-), CKAE1/ AE3(-/+), EMA(-/+), Ki67(+) w 90% of cells; cancer [EA(-), p63(-), p40(-), Chromogranin A(-), Synaptophysin(-)], melanoma [S100(-), SOX10(-)], lymphoma [CD20(-), PAX5(-), CD3(-), CD30(-), ALK1(-), CD43(-), CD23(-), CD5(-), BCL6(-), CyclinD1(-), CD31(-), CD33(-), CD34(-), EBER-ISH(-), CD68(-), CD163(-)], other sarcomas [CD117 (-), DOG1(-), SMA(-), Caldesmon(-), Calretynin(-)] were excluded and epithelioid rhabdomyosarcoma was diagnosed. Conclusion: Epithelioid RMS are rare, localized mainly in soft tissues (our case is second for the gastrointestinal tract), affecting elders and clinically aggressive tumours. The diagnosis is challenging because of carcinoma, melanoma, and lymphoma mimicry. Crucial for correct classification is the high expression of desmin, with variable MyoD1/ Myogenin positivity; remarkably, in some cases, cytokeratins could be aberrantly seen. The immunohistochemical stains still remain an essential step of diagnosis; further molecular analysis is needed for a better understanding of epithelioid RMS pathogenesis. E-PS-22-025 Chondrosarcoma of the ribs: a report of 6 cases W. Majdoub*, K. Ben Lazreg, S. Mestiri, D. Benletaifa, A. Bdioui, O. Belkacem, L. Jaidane, M. Krifa, S. Hmissa *Pathology Department Sahloul Hospital, Tunisia Background & objectives: Chondrosarcoma is the second most com- mon sarcoma of bone, arising in the pelvis or long bones. It is rare for chondrosarcoma to arise in the rib. We aim to provide a clinico- pathological description of chondrosarcoma of the ribs (CSR). Methods: we conduct a retrospective study of 6 patients diagnosed with CSR listed in the Cancer Registry of Center Tunisia during a period of 16 years from 2006 to 2022. All cases were diagnosed on surgical resection specimen. Results: There were 4 males and 2 females. The mean age was 45 ans with extremes of 19 and 67 ans. In four cases the tumour was local- ized on fourth, fifth and sixth ribs and in two cases the tenth rib was involved. Median size was 11 cm and ranged from 4 to 23 cm. A radical excision with widely negative microscopic margins was performed in