ECP 2023 Abstracts

S293 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 E-PS-12-044 Sarcoma mimicking an epithelial malignancy in the head and neck: a cytomorphological diagnostic challenge M. Munonyara*, A. Sandison *Guy’s and St Thomas’ Hospitals NHS Foundation Trust, United Kingdom Background & objectives: Spindle cell/sclerosing rhabdomyosarcoma (SRMS) is a rare sarcoma in adults with a predilection for the head & neck. We present a case of a buccal SRMS mimicking epithelial malignancy clinically and on FNA cytology. Methods: A 24-year-old man presented with a 3/52 history of left facial swelling and pain. A 3cm fluctuant swelling was present in the oral cavity and FNAC was performed. The cytology showed clusters of irregular, hyperchromatic, basaloid neoplastic cells, some arranged in a luminal formation with stroma. Based on the location and cytomor- phology, the initial diagnosis was primary salivary gland neoplasm. Results: Staging CT scan revealed a 5cm lobulated buccal tumour extending into the deep buccal space and eroding the dorsal wall of the ipsilateral maxillary antrum. A core biopsy sent for histology showed small round and spindled tumour cells arranged in a pseudo- micro alveolar pattern within hyalinised stroma. Occasional mitotic figures were present but no necrosis. On immunohistochemistry the tumour expressed desmin, myogenin and MyoD1. FOX01 gene rearrangement was not detected on FISH. The histological diagnosis was SRMS. Conclusion: SRMS is rare and challenging to diagnose on cytology and histology. Clinically and histologically they can mimic epithelial tumours including basaloid cell neoplasms and myoepithelial tumours. Routinely, FNAC is the first diagnostic test when assessing head and neck lesions. Therefore, awareness of SRMS presenting in this loca- tion is imperative as it mimics epithelial malignancy. Sarcoma, such as SRMS should be considered in the differential diagnosis of a head and neck lesion showing aggressive radiological features and rapid onset of symptoms. E-PS-12-046 Human papillomavirus (HPV)-related multiphenotypic sinonasal carcinoma: analysis of three cases with uncommon HPV subtypes J.H. Nam*, Y. Choi *Chonnam National University Hospital, Republic of Korea Background & objectives: Human papillomavirus (HPV)-related mul- tiphenotypic sinonasal carcinoma (HMSC) is a newly emerged tumour restricted to the sinonasal tract and associated with high-risk HPV. We describe a pathologic features of HMSC and draw attention to the uncommon HPV subtypes in given cases. Methods: We described 3 HMSC cases diagnosed at our hospital. We will describe the epidemiology and unique pathologic features, discuss its distinction from other tumours including adenoid cystic carcinoma and squamous cell carcinoma. Immunohistochemical stains for p16, c-kit, p63, and SOX-10 were performed along with HPV DNA test in all 3 cases using PANA RealTyper™ HPV Kit (PANAGENE Inc., South Korea). Results: All cases were from men aged 60 to 86 years (mean, 75), and all tumours were larger than 3cm in size (mean, 4cm). Histologi- cally, solid nests of basaloid cells and cribriform pattern were the main characteristics. Every case demonstrated atypia of surface squamous epithelial layer, morphologically similar to the squamous cell carci- noma in situ. All 3 cases showed strong, diffuse positivity for p16, and it is noteworthy that positive results were also obtained in the surface squamous epithelial layer, including the lesion showing the atypical change. As a result of the HPV DNA test, all three cases had different high-risk HPV subtypes (18, 56, and 82, respectively). Conclusion: Majority of HMSC cases published are from the west, and HPV subtype testing confirmed that HPV type 33 was the most common subtype. These results may suggest the possibility that the dominant HPV subtypes of HMSC in East Asia are different from those in the West. Still, an accurate interpretation is difficult due to the lim- ited number of cases. E-PS-12-047 The first reported case of intraparotid ganglioneuroma masquer- ading as a malignancy B. Othman* *Charles University, Czech Republic Background & objectives: Ganglioneuromas (GNs) are slow-growing, benign tumours arising from Schwann cells and ganglion cells. The incidence of GNs is extremely rare, especially in the head and neck. We herein describe the first reported case of intraparotid ganglioneuroma masquerading as a malignancy. Methods: We report a 42-year-old female presented with a parotid mass. The case was diagnosed mainly based on morphology. Results: The excised lesion revealed two intermingled cell popula- tions with variably trabecular or pseudoglandular architecture: large, rounded cells with an abundant, finely granular eosinophilic cytoplasm, and fasciculated cells with an elongated cytoplasm featuring fine fibril- lar extensions. No mitosis or tumour necrosis was observed. Perineural entrapment, areas of colliding neuronal components, and granular gan- gliocytes were conspicuous. Immunohistochemical staining for S100, synaptophysin, and chromogranin A were positive. Nonetheless, no immunoreactivity for cytokeratins (CK5/6, CK7, AE1/AE3), epithe- lial membrane antigen, HMB45, Melan A, CD30, calponin, SSTR2A, DOG-1,TTF-1, CD117, and p40 was detected. The lesion was excised after nerve dissection to preserve the motor nerve fibres; the frozen section revealed margins to be free from neoplasms. Conclusion: We emphasize the possibility of the development of ganglioneuroma inside the parotid gland. Caution should be taken to avoid diagnosing this benign lesion as a metastatic malignancy (e.g. neuroblastoma) or requesting unnecessary aggressive treatment (e.g., postoperative chemotherapy and radiotherapy). E-PS-12-048 Insights into investigating the pathogenesis of salivary carcinoma ex adenomas with taxonomical implications B. Othman* *Charles University, Czech Republic Background & objectives: Carcinomatous transformations are com- mon atop (monomorphic) basal cell, canalicular, and/or pleomorphic adenomas. Nonetheless, the prognostic value of a newly developing malignancy is variable. This study underpins the literature for outlin- ing malignant transformations with reference to morphologic changes. Methods: After mining the published literature for all salivary carci- nomas arising in benign lesions from 2014 to 2022, we annotated each carcinoma for the marker(s) used and the level of evidence attained for diagnosing each published case. Questionable diagnoses were discarded. Results: The term ’salivary carcinoma ex mixed adenoma (CXMA)’ is proposed as a generic term that clusters, at least, 63 malignant sub- types. Each subtype could reveal one or many mutations drivers that pertain either to a known molecular profile of the malignant component or molecularly unlabled malignancy developing secondary to a pre- existence mixed adenoma. Conclusion: Coining new designations for known pathologic enti- ties featuring unreported morphological variations without significant change in clinical behaviour is as beguiling as considering all salivary gland malignancies either low-grade or high-grade. With using the umbrella term CXMA, either mesenchymalizing, reprogramming, transdifferentiating or, with lineage plasticity, to encompass all mixed