ECP 2023 Abstracts

S222 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 NY-ESO1-positive GBC could be potential candidates for the immu- notherapy. Additional research is needed in this direction due to the low frequency but high mortality of these tumours. E-PS-07-014 Myxoid hepatocellular adenoma of the liver: a rare, diagnostically challenging case S.K. Dursun*, Z.B. Erdem, İ. Özden, M.B. Yilmaz Ozguven, N. Dur- sun Kepkep *Basaksehir Cam and Sakura City Hospital, Turkey Background & objectives: Hepatocellular adenomas (HCAs) are benign neoplasms of the liver that are classified into four major groups in the current WHO classification. In addition to these, rare subtypes with distinct clinical behaviour such as myxoid HCAs, are believed to exist. Methods: We report a case of 35-year-old male, presented with abdom- inal pain 10 years ago and was diagnosed with hepatosplenomegaly and multiple hepatic masses. Radiologic diagnosis was haemangiomas and follow-up was recommended but patient failed to attend appointments. Due to worsening sypmtoms, he presented at clinic where imaging revealed enlarged masses. Left hepatectomy was performed with dif- ferential diagnosis of epitheloid haemangioendothelioma. Results: The liver was enlarged with 10 well-defined tumour nodules (0,3 cm to 10 cm) on the gross examination. Histomorphological eval- uation of the nodules showed hepatocytes with minimal cytological & architectural atypia, forming cords on the background of the extensive myxoid stroma. Occasional peliosis-like areas, aberrant veins, and macrovesicular steatosis were also present. Thickening of hepatocyte plates, increased mitosis, or necrosis was not found. Morphological features, as well as immunohistochemistry results, were consistent with well-differentiated hepatocellular neoplasm. Molecular analysis (NGS) was also performed; HNF1a mutations were detected. Morpho- logical findings with supporting immunohistochemical & molecular analysis results confirmed the diagnosis of “Myxoid variant HCA, HNF1A-inactivated subtype”. The patient has no recurrence after 5 months of follow-up. Conclusion: The myxoid subtype of HCA has been recently identified and it remains unclear whether it is specific to a known HCA sub- type. It has distinct histomorphological features. Although it is a newly recognized subtype, recent literature has emphasized the higher risk of malignant transformation, highlighting the importance of accurate classification. Our case of a myxoid HCA, with supporting molecular analysis, highlights the need for awareness of this extremely rare vari- ant’s histomorphological features for improved treatment modalities. E-PS-07-015 What is hidden behind focal lesions of the pancreas - our two and a half years of experience A. Đikić Rom*, K. Eric, M. Andrejevic, M. Dimic Cumic, V. Dugalic *Department of Pathology, Pathohistology and Medical Cytology, Uni- versity Clinical Centre of Serbia, Serbia Background & objectives: The pancreas is a complex organ that may give rise to various lesions which have significant clinical/radiologi- cal overlap with neoplastic lesions. It has been shown that 5-10% of pancreatectomies with a clinical diagnosis of pancreatic cancer, are basically non-neoplastic lesions. Methods: Our study included 210 patients with preoperative clinically/ radiologically verified focal pancreatic lesion, operated on at the Diges- tive Surgery Clinic, and histopathological diagnosis of the operative material was made at the Department of Pathohistology, University Clinical Centre of Serbia, in the period from January 2018 to June 2020. After the classification of the lesions, appropriate statistical analysis methods were applied. Results: Based on morphological and immunohistochemically characteristics, the obtained samples were classified into two major categories: primary and secondary pancreatic lesions. Primary pan- creatic lesions were identified in 98.1% of the total number of oper- ated patients. These lesions were divided into five major categories, namely: 1) malignant epithelial tumours of the pancreas: 52,64%; 2) malignant epithelial tumours of the distal part of the common bile duct: 19,14%; 3) malignant epithelial tumours of the ampullary and periampullary region: 15,31%; 4) neoplastic precursor lesions of the pancreas: 7,65% and 5) pseudotumour and benign pancreatic lesions: 5,26%. Secondary (metastatic) pancreatic lesions accounted for 1.9%, and in all cases, it was about metastatic renal cell carcinoma. Conclusion: A heterogeneous group of pancreatic pathology, which can mimic primary pancreatic neoplasms, consists of pancreatic pseudotumour lesions, small group of rare benign pancreatic tumours and secondary pancreatic lesions. The variety of pancreatic lesions presents a challenge to clinicians/radiologists, because operations are often planned only based on the results of imaging methods in combination with the clinical presentation, but without preoperative pathohistological diagnosis. Misdiagnosis of these entities as neo- plastic lesions of the pancreas can lead to unnecessary and extensive operations. E-PS-07-017 Looking beyond the obvious: non-vascular mesenchymal tumours of the adult liver Z.B. Erdem*, S.K. Dursun, S. Bagbudar, E. Kinaci, M.B. Yilmaz Ozguven, N. Dursun Kepkep *Basaksehir Cam and Sakura City Hospital, Turkey Background & objectives: Vascular tumours are the most common primary mesenchymal tumours of the liver both on malignant and benign end of the spectrum. Although exceedingly rare, other mes- enchymal tumours can arise in the liver which makes it difficult to differentiate. Methods: Aim of this study is to highlight these extremely rare enti- ties and their histopathologic differential diagnoses based on real- life cases. All liver samplings, performed due to the presence of a hepatic mass and evaluated at a single centre, between May 2020 to March 2023, were retrieved from pathology files (n=592). Pri- mary mesenchymal tumours were evaluated according to their line of differentiation. Results: Of all liver tumours, 24 were confirmed histomorphologi- cally to be of mesenchymal origin(4.1 %). Of these, seven were non- vascular. The reported entities were as follows: malignant solitary fibrous tumour (n=1), inflammatory myofibroblastic tumour (n=1), rhabdomyosarcoma (n=1), leiomyosarcoma (n=2), undifferentiated embryonel sarcoma (UES)(n=2), epitheloid haemangioendothelioma (n=4), angiosarcoma (n=1), and benign vascular proliferations (hae- mangioma etc.)(n=12). A broad immunohistochemistry panel, and if needed, molecular diagnostics were performed to aid in accurate differ- ential diagnosis. The patients were equally distributed between genders (F/M: 1) with a mean age of 50,6 years (20 to 89 years). All tumours were confirmed to be primary following systemic evaluation. Both of the UESs found to have arisen on the background of a mesenchymal hamartoma. Conclusion: Vascular tumours are the most well-known mesenchymal tumours of the adult liver. Usually, benign vascular tumours are diag- nosed and monitored radiologically without the need for histopatholog- ical confirmation. However, in some cases, radiological diagnosis can be misleading. While histopathological diagnosis is the gold standard and essential for proper patient management, it can be challenging due to the rarity. This study discusses tips and potential pitfalls that may be encountered in routine practice to ensure accurate diagnosis and precise patient care.