OBJECTIVETo study the morphologic and immunohistochemical features of gastrointestinal stromal tumors (GISTs) and to explore the reference parameters for malignancy.

METHODSSeventy six (76) cases of primary GISTs were distinguished from a group of gastrointestinal mesenchymal tumors by use of a panel of antibodies such as CD117, CD34 by immunohistochemical EnVision method, their biologic behaviors were analyzed by including their follow-up data.

RESULTSAll patients were adults, age range 32 to 81 years (mean 54 year), male 39 cases and female 37 cases; the tumors were situated in stomach (36 cases), in small intestine (23 cases), colon (2 cases) and rectum (15 cases). The most common symptoms were abdomen mass, vague pain and GI bleeding. Forty eight (48) cases were mainly located within the muscularis propria, 25 cases outside the serosa, and 3 cases below the mucosa. Grossly, they were of soft consistency often with hemorrhage, cystification or necrosis. Microscopically, the tumors were composed of spindle cells (46 cases) or epithelioid cells (9 cases) and of both cells (21 cases), arranged in interlacing fasicles, diffusing sheets, pallisading, whirling, alveolar and giant pseudo-rosette shapes. Tumor cells often had abundant cytoplasm with light to moderate eosinophilic or slight basophilic in staining, the nuclei generally showed spindle, blunted ends, round or signet in shape with nucleoli. Immunohistochemically, CD117 and CD34 showed diffuse strong expression, the positive rates were 98.7% and 68.4% respectively, alpha-SMA, MSA, S-100, PGP9.5 showed focal expression, the positive rates were 25.0%, 19.7%, 23.7% and 17.1% respectively, vimentin were all positive and desmin, GFAP, NF were all negative. Nine cases were benign, 19 cases borderline and 48 cases malignant. Follow-up of 20 cases with benign and borderline tumors found patients alive without tumor. In the malignant group of 34 cases, 10 cases were alive without tumor, 10 cases developed recurrence or metastasis, and 14 cases died of tumor. Coagulative necrosis, mitotic activity over 10/50HPF, high cellularity and obvious pleomorphism were all in the malignant group. In this group, tumor necrosis, adhesion in operation, tumor, over 5 cm in diameter, mitotic activity over 5/50HPF had significant differences among three groups and the 3 years survival rate had a significant difference in tumors with or without coagulative necrosis and also in tumors with or without mitotic activity over 5/50HPF.

CONCLUSIONSGISTs predominantly occurred in middle aged or old patients, the tumors had varied cell types and different arrangements, the immunohistochemical characters were positive for CD117 and CD34, negative for desmin, occasional positive for alpha-SMA, MSA, S-100 and PGP9.5, which were helpful to differentiate GIST from leiomyomas and Schwannomas. Coagulative necrosis, mitotic activity over 10/50HPF, high cellularity with obvious pleomorphism were also helpful parameters for diagnosis of malignancy aside from metastasis and invasion. Adhesion, over 5 cm in diameter and mitotic activity over 5/50HPF but less than 10/50HPF might be the potential malignant parameters.