Intra-abdominal desmoid tumor difficult to distinguish from a gastrointestinal stromal tumor: report of two cases.

Desmoid tumors are benign fibroblastic neoplasms with no metastatic potential, but a propensity for local recurrence even after complete surgical resection. These lesions can develop at any site in the body, and commonly occur in the intra-abdominal area. Intra-abdominal desmoid tumors usually occur at the mesentery or retroperitoneum, and may morphologically mimic gastrointestinal stromal tumors (GISTs). Distinguishing between these tumors is important, because the therapies differ substantially, but is often difficult even with the use of CD117 staining. We herein report the cases of two patients with sporadic intra-abdominal desmoid tumors that were differentiated from GIST by immunohistological examination using beta-catenin and CD34. Desmoid tumors specifically express nuclear beta-catenin, and show no expression of CD34. We recommend staining for beta-catenin and CD34 when an intra-abdominal desmoid tumor is suspected.