Solid-Cystic Pancreatic Tail Desmoid Tumor with Beta-Catenin Positivity

A 19-year-old Hispanic woman with a history of polycystic ovarian syndrome presented with worsening abdominal pain, nausea, and vomiting. She had stable vitals and lower/suprapubic abdominal pain on exam, as well as a positive urinalysis. She was initially admitted for treatment of a urinary tract infection. An abdominal computed tomography scan, performed due to persistent abdominal pain, revealed a cystic lesion anterior to the pancreatic tail adjoining the splenic flexure and colonic diverticulosis, which was concerning for phlegmon formation (Figure 1). Magnetic resonance imaging showed a 4.1-cm pancreatic tail soft tissue lesion with a 3.4-cm unilocular nonenhancing cystic lesion. Carcinoembryonic antigen and CA19-9 antigen levels were normal. The patient underwent endoscopic ultrasound with fine-needle aspiration of the pancreatic lesion, and histopathology showed uniform spindle-cell proliferation (Figure 2). A colonoscopy, performed to exclude colonic involvement, had unremarkable gross findings. Laparoscopic distal pancreatectomy, splenectomy, partial gastrectomy, and partial segmental colectomy were performed. Gross examination revealed an infiltrative poorly circumscribed 4-cm mass with a 2.5-cm unilocular cystic area (Figure 3). Immunohistological evaluation led to a diagnosis of desmoid tumor primarily involving the pancreas, with cells showing nuclear positivity to beta-catenin. The patient recovered well postoperatively and was discharged with follow-up with a genetic counselor