ECP 2023 Abstracts

S284 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 E-PS-12-007 Sinonasal non-intestinal type adenocarcinoma with clear cell fea- tures: a morphologic and immunohistochemical study G. Arcovito*, I. Dallan, A. Franchi *University of Pisa, Italy Background & objectives: Occasionally, sinonasal non-intestinal- type adenocarcinomas (non-ITAC) present with clear cell morphol- ogy, including cases that may closely mimic renal cell carcinoma. The aim of our study is to perform a histologic and immunohistochemical analysis of sinonasal clear cell non-ITACs. Methods: We searched our institutional files for sinonasal non-ITAC and we selected those presenting clear cell morphology. All available histologic slides and formalin fixed paraffin embedded tissue blocks were retrieved. The immunohistochemical panel applied to all cases included pancytokeratin, cytokeratin 7, S100, calponin, smooth muscle actin (SMA), P40, carbonic anhydrase IX (CAIX), PAX8 and RCC. Results: Three cases were identified. The patients were 2 females and 1 male of 44, 80 and 63 years, respectively. All lesions were in the nasal cavities and were surgically treated. Two patients experi- enced local recurrence at 40 and 67 months. Histologically, all lesions were formed by a uniform population of epithelioid cells with clear cytoplasm organized in small nests separated by thin fibrous septa. In addition, 2 tumours presented areas with papillae lined by cuboidal or cylindrical cells with pale eosinophilic cytoplasm. All cases were posi- tive for pancytokeratin, cytokeratin 7 and P40; 2 cases were positive for S100, while calponin was focally expressed. SMA, CAIX, PAX8 and RCC were negative. Conclusion: We report a subset of sinonasal non-ITAC with clear cell features that appear to differ from the so-called sinonasal renal cell– like adenocarcinomas for their histologic and immunohistochemical profiles, including absence of CAIX expression. Our results, including S100 and P40 positivity and focal calponin expression, suggest a puta- tive myoepithelial differentiation in these tumours. Funding: This study was partly supported by funds from Tuscany Health Service (ADAPTA project) to AF E-PS-12-008 Primary head and neck paraganglioma cell culture expresses markers of cancer and mesenchymal stem cells I. Bakhtogarimov*, M. Fedorova, A. Kobelyatskaya, A. Ayupova, V. Pavlov, A. Kudruavtseva, A. Snezhkina *EIMB RAS, Russia Background & objectives: Head and neck paragangliomas (HNPGLs) are highly hereditary neuroendocrine tumours that poorly investigated due to their rarity. At present, there is no commercially available HNPGL cell culture, due to the complexity of neuroendocrine tumour cell cultivation. Methods: Primary cell culture was derived from patients with HNPGL and subjected to immortalization through the expression of human TERT (hTERT). After selection, cell culture was categorized by sin- gle cell expression profiles using 10X Genomics. Single cell sequenc- ing was performed on Illumina NextSeq 2000 System. Bioinformatics analysis was carried out using Cell Ranger. t-SNE method was used for clustering and visualization. Results: Cell types of HNPGL culture were annotated based on sin- gle-cell RNA-Seq data using cCATCH toolkit. Expression of cluster marker genes were matched with CellMatch reference database that includes 353 cell types and 686 related subtypes associated with 184 tissue types. We found that 55% and 35% of studied cells expressed markers of cancer and mesenchymal stem cells, respectively. As an alternative, we used PollenGliaData RNA-Seq dataset and revealed that almost all cells (91%) also showed expression of radial glia mark- ers. Analysis of cell cycle phase was done with Seurat; the majority of cultivated cells were in G1-pahse (53%), followed by S-phase (28%), and G2M-phase (19%). Conclusion: We could conclude that primary HNPGL cell culture is characterized by expression profiles close to cancer and mesenchymal stem cells. This is to agree with the evolution origin of paraganglia from multipotent mesenchymal stem cell. Extension of G1-phase could be associated with transition from undifferentiated phenotype of cells to differentiated one. This work was financially supported by a grant from the Russian Sci- ence Foundation (no. 21-14-00353) and performed using the equip- ment of the EIMB RAS “Genome” centre ( http://www.eimb.ru/rus/ckp/ ccu_genome_c.php). E-PS-12-009 An infrequent case of odontogenic myxoma of the maxilla in a 28-year-old female M. Barbesier*, L. Christe, S. Sancho, S. Berezowska *Institute of Pathology, Lausanne University Hospital (CHUV) and University of Lausanne, Lausanne, Laboratoire Promed, Marly, Switzerland Background & objectives: Odontogenic myxoma (OM) is an uncom- mon benign odontogenic neoplasm of the jawbone. The diagnosis of this entity poses a challenge because its clinical and radiological manifestations are non-specific and often lead to confusion with other benign and malignant neoplasms. Methods: A 2 cm osteolytic lesion of the maxilla was discovered radiographically in 28-year-old women who presented with painless jaw swelling. Microscopically, the tumour consisted of a hypocellular proliferation of bland spindled to stellate cells set in myxoid stroma, without islands of odontogenic epithelium. The diagnosis on biopsy was followed by a surgical excision with tumour free margins. Results: Histomorphology allowed the diagnosis of an odontogenic myxoma on biopsy. OM of the jaw is a rare benign, but locally aggres- sive odontogenic neoplasm, mainly affecting younger adults, with marked female predilection. The mandible is more frequently affected than the maxilla. It comprises 0,5% of all bone tumours and 3-6% of odontogenic tumours. These tumours originate from the primitive mes- enchymal portion of the developing tooth. Because of its slow growth, OM is often asymptomatic. However, OM is associated with a high recurrence rate ranging from 10% to 43% (mean 25%). Thus, surgical excision is the treatment of choice, but without agreement on surgical margins. Conclusion: OM is diagnosed according to H&E histomorphology. Due to the unspecific nature of the clinical and radiological presenta- tion, histology plays a major part in the diagnosing OM, especially to exclude the others differentials diagnoses, and particularly the malignant neoplasms that could be initially suspected by the locally aggressive behaviour of these tumours. Moreover, histological diag- nosis allows adequate surgical management of the patient, in order to reduce the known risk of tumour recurrence. E-PS-12-010 Laryngeal spindle cell carcinoma: a diagnostic challenge. Review of cases from the last 23 years in a tertiary hospital G. Barrios Millán*, E. Ruiz-Bravo *Hospital Universitario La Paz, Spain Background & objectives: Spindle cell carcinoma (SCC) of the head and neck represents a diagnostic challenge due to its overlap, both mor- phological and immunohistochemical, with other benign and malignant entities. Our objective is to review the histopathology of the cases diagnosed in our centre. Methods: A retrospective review of the cases diagnosed as SCC in our hospital from 2000 to 2023 was carried out. The histopathological