A Rare and Clinically Aggressive Desmoid Tumor Invading the Pancreas Diagnosed by Endoscopic Ultrasound: Case Report

Introduction: Desmoid tumors invading the pancreas are rare. Preoperative diagnosis is uncommon either because a more common malignant lesion is suspected in a symptomatic patient that is submitted to surgery without tissue acquisition or biopsies are inconclusive given the variable cellularity of specimens obtained and difficult differential diagnosis. Only one case of successful diagnosis by endoscopic ultrasound-guided biopsies has been reported to date. Case Presentation: A 30-year-old male patient, followed for familial adenomatous polyposis with a past medical history of prophylactic proctocolectomy, presented in a routine abdominal ultrasound unilateral calyceal dilation. Further imaging studies described a 65 mm nodular, infiltrative, hypodense, neoplastic lesion, centered at the distal body and tail of the pancreas, enveloping the splenic vein, and a second similar lesion near the right common iliac vessels. The patient was asymptomatic and laboratory results were normal. The pancreatic mass was biopsied guided by endoscopic ultrasound, and cythopathological analysis concluded that desmoid fibromatosis was the most likely diagnosis. Three weeks post-biopsy, the patient had a rapid and severe clinical progression, with acute abdominal pain, hemorrhagic shock and active bleeding on imaging, demanding emergent exploratory laparotomy and extensive resection of the tumor, which involved the pancreatic tail and invaded adjacent structures. Histopathological analysis of the surgical specimen confirmed the preoperative diagnosis of desmoid fibromatosis. Given the R1 resection and the presence of a second large intra-abdominal lesion, the patient started systemic therapy with vinorelbine. Exocrine pancreatic insufficiency was diagnosed after surgery, with need of enzymatic replacement therapy. Conclusion: Endoscopic ultrasound-guided biopsies can play an important role in the diagnosis of pancreatic desmoid tumors, allowing for nonsurgical diagnostic work-up as surgical resection is no longer considered the first-line therapy.