Sporadic desmoid tumor. An exceptional cause of cystic pancreatic lesion.

CONTEXT Desmoid tumors are rare, benign soft tissue tumors, characterized by the proliferation of fibroblasts in an abundant collagen extra-cellular matrix. Intra-abdominal forms involve the mesentery and retroperitoneum and usually occur associated with familial adenomatous polyposis or Gardner's syndrome. Sporadic cases are more uncommon. Although desmoid tumors do not metastasize, their evolution can be life-threatening due to aggressive local invasion, such as mesentery involvement. CASE REPORT We herein report a very rare location of sporadic desmoid tumors involving the pancreatic tail, presenting as a cystic lesion. A 51-year-old woman presented with recurrent abdominal pain and weight loss. The diagnosis of mucinous cystadenocarcinoma was suspected preoperatively and the patient underwent a splenopancreatectomy with en-bloc resection of the left colonic flexure, duodenojejunal junction and part of the posterior gastric wall. Pathological analysis revealed fibroblastic proliferation arising in musculoaponeurotic structures consistent with a desmoid tumor. The diagnosis was confirmed by immunocytochemical analysis and the assessment of the beta-catenin gene mutation. Perioperative examination reported gastric and small-bowel invasion. No treatment was given postoperatively to prevent desmoid tumor recurrence. After a 1-year follow-up, no recurrence was observed. CONCLUSION Desmoid tumors are very rare in the pancreas and their diagnosis can be difficult, such as in our case where it presented as a cystic lesion. In contrast to intra-abdominal forms, sporadic pancreatic desmoid tumors are more frequent than those associated with familial adenomatous polyposis.