ECP 2023 Abstracts

S366 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 accompanied by small segments of muscle and adipose tissue, without history of cutaneous or mucosal melanocytic lesions. Results: On microscopic examination, the tumour segments consisted of compact aggregations and nests of homogenous, epithelioid or spin- dle-shaped cells, with high nuclear atypia, eosinophilic and focally amphiphilic or clear cytoplasm, with medium-sized vesicular nuclei and apparent nucleoli, in a relatively sclerotic stroma. 23 mitoses / 10 HPF were counted and there were focal extracellular melanin deposi- tions and necroses. Also, tumour cells were infiltrating between muscle fibres and fat cells. The immunohistochemical control of the neoplasm revealed strong expression of S-100, HMB-45, MART-1 and negativity for cytokeratins, WT-1, Calretinin, TTF-1, Synaptophysin, Chromogra- nin, NSE and BRAFV600E. Also, fluorescence in situ hybridization was positive for EWSR1 gene translocation. Conclusion: Clear cell sarcomas are mesenchymal tumours, classi- fied as tumour of uncertain differentiation in WHO 2020, which occur very rarely in the mediastinum. The diagnosis of these type of sar- comas is challenging, because of the morphological similarities with melanoma. In our case, the lack of previous cutaneous or mucosal melanocytic lesions and the positivity of fluorescence in situ hybridi- zation for EWSR1 gene translocation, lead us to the diagnosis of this type of sarcoma. E-PS-23-009 A case of thoracic SMARCA4-deficient undifferentiated tumour E. Psychogiou*, P. Tziakou, P. Megas, M. Miliou, K. Papadopoulou, A. Konstantinidou, E. Papadopoulou, D. Riga, C. Glava, I. Vamvakaris *General Hospital of Athens Sotiria, Greece Background & objectives: Thoracic SMARCA4-deficient undifferen- tiated tumours are aggressive neoplasms that most commonly occur in the mediastinum of male smokers. SMARCA4 is considered a tumour suppressor gene, both the loss of protein expression as well as protein upregulation have been associated with neoplasia. Methods: A 54-year-old man with free medical history was admitted to our hospital after the diagnosis of a mediastinal mass at CT scan. Biopsy was performed by thoracic surgeons for the determination of the nature of the tumour. Results: Histopathologically, the tumour had a solid architecture pat- tern, comprising of medium-sized and larger cells, with dark-coloured round to oval nuclei, prominent nucleoli and basophilic cytoplasm, mild pleomorphism, extensive necrosis and very high mitotic activity. Plenty of lymphocytes were observed. Based on morphologic features and location of the mass the differential diagnosis includes non-small cell carcinoma, sarcoma, malignant melanoma, lymphoma, and malig- nant mesothelioma. Immunohistochemistry study demonstrated posi- tive expression of RB and KLMW, while there was negative expression of TTF-1, P40, CD56, CK7, CD30, PLAP, S-100, NUT and loss of SMARCA4. This immunoprofile in association with the location of the mass supports a diagnosis of SMARCA4-UT. Conclusion: SMARCA4-UT, formerly called “SMARCA4-deficient thoracic sarcoma” are very aggressive tumours and are characterized by a poorly differentiated morphology with at least a subset of these tumours exhibiting focal rhabdoid features. While the immunophenotype can vary, in general these tumours show no or only focal keratin expres- sion. Loss of expression of BRG1 is the hallmark of these tumours. The diagnosis of these tumours is important as preclinical and early clinical trials using enhancer of zeste homolog (EZH2) inhibitors are promising. E-PS-23-010 Glomus tumour of the trachea: a rare finding N. Stavrinou*, F. Dolkiras, P. Vlachou, A. Therapontos, M. Lenos *Department of Pathology, Evaggelismos General Hospital Athens, Greece Background & objectives: Glomus Tumour is a neoplasm which usually arises on superficial and rarely on deep locations. Its cells resemble modified smooth muscle cells of the normal glomus body. Few cases of glomus tumour arising on the tracheobronchial tree have been reported. Methods: We report a case of a 75-year-old man who presented with dyspnea. A tracheal mass was recognized during bronchoscopy and sur- gery was performed. The specimen received by the pathology depart- ment was a tracheal segment consisting of 3 cartilaginous rings, with an identifiable luminal exophytic mass measuring 1,8 cm. Results: Microscopic evaluation of the tumour revealed a neo- plasm consisting of uniform eosinophilic cuboidal cells arranged mostly in nests. Fibrovascular septa and foci of haemorrhage were also identified. Mitoses were rare (1/50HPF), and necrosis was not observed. Immunohistochemical analysis was positive for SMA and h-caldesmon, whereas AE1/AE3, CK 8-18, CK7, p40, Synaptophysin, Chromogra- nin, CD34, CD31, TFE3, MelanA, HMB45 were negative. Conclusion: Glomus tumours are classified into three histopathologic categories (benign, tumours of uncertain malignant potential, malig- nant tumours) according to strict histopathologic criteria (deep loca- tion, size > 2cm, mitotic rate >5/50 HPF, marked nuclear atypia). The vast majority is associated with a benign biologic behaviour. However, in the current case due to its deep location the lesion was diagnosed as “Glomus tumour of uncertain malignant potential”. Due to their rare occurrence, follow up guidelines for tracheobronchial glomus tumours are not well established. E-PS-23-011 Ectopic cervical thymus in a patient with oral squamous cell car- cinoma: a diagnostic pitfall D. Tapoi*, A. Dumitru, A. Ciongariu, I.A. Dandu Colceriu, D. Dumitrescu, V. Ionita, C.C. Badiu, M. Costache *University Emergency Hospital, Romania Background & objectives: Ectopic cervical thymus is a relatively fre- quent finding in children and is the result of an incomplete migration of the thymic tissue during embryogenesis. However, remnants of thymic tissue are a rare and usually incidental encounter during adulthood. Methods: We present the case of a 55-year-old woman who presented to hospital for an exophytic, ulcerative palatine tumour. Upon physi- cal examination, several enlarged lymph nodes were discovered in the cervical region, which were excised along with the tumour. The aim of our study is to gain further insight into tumours of the head and neck and discuss unusual differential diagnoses. Results: Upon histopathological examination, the palatine tumour was diagnosed as an invasive keratinizing squamous cell carcinoma extending into the chorion of the mucosa. The lateral cervical lymph nodes showed only reactive changes for the most part, but one of them exhibited nests of squamous cells with keratinization phenomena. This finding prompted further immunohistochemical testing. p63 was posi- tive in the squamous nests and in scattered epithelial cells, and p16 was negative throughout the tissue. The lymphocytes were positive for CD1a but negative for CD20. Thus, the diagnosis of ectopic thymic tissue was established instead of a squamous cell carcinoma metastasis in a lymph node. Conclusion: Ectopic thymic tissue is a rare finding and is usually not included in the differential diagnosis of neck tumours, especially in adulthood. Furthermore, it is usually easily diagnosed solely on histo- pathological features. However, given the context of regional or adja- cent squamous cell carcinomas, it should be taken into consideration and ancillary testing should be performed to establish a certain des- ignation for any lesion with a morphology that bears the hallmarks of squamous differentiation.