S3223 Solitary but Not Silent: When a Pancreatic Mass Reveals a Rare Diagnosis

Introduction: Solitary fibrous tumors (SFTs) are rare mesenchymal neoplasms, most often arising in the thoracic cavity, with approximately 20% found in the abdominal cavity. Pancreatic involvement is infrequent, with only a few reported cases. Unlike thoracic SFTs, pancreatic SFTs show no sex predilection and are typically present around age 60, most often in the pancreatic head. These tumors are usually discovered incidentally or during the evaluation of vague abdominal symptoms and rarely with obstructive jaundice. Diagnosis can be difficult due to nonspecific imaging features and overlap with other pancreatic tumors. Most are diagnosed after surgical resection, although endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) has rarely been reported as a diagnostic method. We report a rare case of pancreatic SFT diagnosed by EUS-FNA. Case Description/Methods: An 87-year-old man with atrial fibrillation presented with abdominal pain, belching, and bloating. A computed tomography revealed a lobulated mass with low attenuation, suggesting necrosis, arising from the pancreatic head and extending into the mesentery, compressing the duodenum without invasion. EUS showed a large, rounded, heterogeneous lesion with central necrosis and prominent vascularity. FNA was performed; the rest of the pancreas appeared normal. Histology showed spindle cell proliferation. Immunohistochemistry (IHC) was positive for STAT6, CD99, and Bcl-2, confirming the diagnosis of SFT. The patient declined surgery and opted for oncology surveillance. Discussion: This case of a rare pancreatic SFT diagnosed via EUS-FNA, is among the few cases reported in the literature using this method. Although imaging lacks pathognomonic features, computed tomography and EUS may reveal findings such as a well-defined hypervascular mass with central necrosis. STAT6 is a key IHC marker supporting diagnosis; CD99 and Bcl-2 may be present but are non-specific. SFTs are called “great simulators” due to variable presentation and nonspecific imaging. Evidence for managing pancreatic SFTs is limited due to rarity, though surgical resection is typically preferred. A 2023 review of 9 resected cases reported no recurrence over a 76-month mean follow-up. The malignant potential has been linked to older age, large tumor size, increased cellularity, mitotic activity, necrosis, and infiltrative borders in SFTs from different locations. Given the limited understanding of malignant potential in this location and absence of surgical resection, close surveillance was recommended for our patient.