Abstract proceedings of Young Talents in Internal Medicine World Contest 2025 (10th McMaster International Review Course in Internal Medicine, May 8–10, 2025, Kraków, Poland; hybrid course)

INTRODUCTIONInternists often investigate complex diagnostic cases that demand interdisciplinary collaboration.We present a rare case of a multivisceral epithelioid vascular tumor associated with an EWSR1::NFATC2 gene fusion.The diagnostic process relied heavily on the integration of anatomo-clinical findings and molecular biology expertise, underscoring the value of collaborative approaches.CASE DESCRIPTION A 39-year-old woman with a history of treated asthma and smoking cessation underwent cholecystectomy.Incidental findings included sclerotic and lytic skeletal lesions, vascular-like hepatic nodules, and peritoneal involvement.Initial histological analysis was nondiagnostic and the patient was lost to follow-up.Two years later, she presented with recurrent exudative ascites requiring repeated paracenteses.Clinical evaluation showed no abnormalities and a good general condition.Routine laboratory tests, including hepatic function and albumin level, were unremarkable.Imaging studies (computed tomography, magnetic resonance imaging, positron emission tomography) showed persistent, mildly hypermetabolic nodular lesions with minimal progression, offering no definitive etiological clues.Transjugular liver biopsy showed normal hepatic architecture, encompassing sinusoidal dilatation, without neoplasia or granulomas.Hepatic catheterization confirmed portal hypertension.Multidisciplinary assessment concluded a diagnosis of noncirrhotic portal hypertension caused by extrinsic compression of hepatic veins, likely from hepatic nodules and peritoneal sheath encasement, mimicking Budd-Chiari syndrome.Comprehensive infectious and immunohematological workups were noncontributory.Laparoscopy showed an inflamed, multinodular peritoneum.Histopathological analysis of peritoneal biopsies showed fibrotic remodeling with minimal inflammation and capillary hyperplasia, which was deemed reactive following a consultation with a national expert.Despite these conclusions, the clinical and radiological presentation suggested the primum movens of a multivisceral microvascular disorder.After multiple inconclusive computed tomography-guided bone biopsies, blind iliac crest bone marrow biopsy identified atypical vascular lesions with ossifying reactions.The case was discussed at a national bone tumor board.Histological findings suggested low grade vascular tumor, but clinical and radiological data were inconsistent.Suggested molecular analysis of a peritoneal biopsy ultimately identified an EWSR1::NFATC2 gene fusion, confirming a rare vascular epithelioid tumor.DISCUSSION This case involved extensive but indolent hepatic, peritoneal, and osseous involvement, which evaded diagnosis despite thorough investigations.Multidisciplinary collaboration and targeted biopsies directed the diagnostic process toward a vascular proliferation.Ultimately, the use of a national network and a specialized molecular biology laboratory led to the identification of a EWSR1::NFATC2 gene fusion, a rare anomaly associated with a spectrum of vascular tumors ranging from malformations and hemangiomas to sarcomas.Molecular biology, a routine tool in TOP 20