OBJECTIVETo explore the clinicopathological, immunohistochemical and molecular genetic features of intra-abdomen extra-gastrointestinal stromal tumors (EGISTs) and their differential diagnosis.

METHODSNine cases of EGISTs from the abdominal cavity or retroperitoneum which were previously diagnosed as leiomyoma, leiomyoblastoma, or leiomyosarcoma etc. by a panel of antibodies such as CD117, CD34, alpha-SMA, MSA, desmin, S-100, and PGP9.5 from which five cases were detected for c-kit gene mutation.

RESULTSThe tumors occurred in 5 men and 4 women, the age ranged from 38 to 72 years (mean 61.7 years). Four cases arose from the mesentery, two from omentum, two from retroperitoneum and one located at the hilus of the spleen. The size of tumors ranged from 5 cm to 23 cm (mean 12.9 cm) in diameter and the tumor cell components varied: mainly spindle cells (seven cases), epithelioid cells (one case), mixed cells (one case). Tumors expressed CD117 (8/9), CD34 (5/9), alpha-SMA (3/9), MSA (4/9), desmin (0), S-100 protein (1/9) and PGP9.5 (1/9). Of the five cases examined for heterozygous deletion mutation of 11 exon of the c-kit gene two were found positive. Two borderline cases showed long-term survival of 8 years and 11 years, respectively. In seven malignant cases, two showed adverse outcome, one survived 4 years without recurrence, two were lost in follow up and two new cases were still being in followed.

CONCLUSIONSGIST-type stromal tumors can also occur in the abdomen, most cases were borderline or malignant, tumor coagulative necrosis, mitoses >or= 5 per 50 high-power fields and obvious nuclear atypia indicating malignancy. Differential diagnosis of EGIST including benign or malignant smooth muscle tumors, benign or malignant nerve sheath tumors etc.