OBJECTIVETo determinate the clinicopathologic parameters in predicting the malignant behavior of gastrointestinal stromal tumor (GIST).

METHODSEight hundred and forty cases of GIST were retrospectively reviewed. The tumors were classified as malignant if they met any of the following criteria: evidence of gross dissemination (including liver metastasis and/or peritoneal spread), evidence of microscopic dissemination (including lymph node metastasis, infiltration to vessels, fat tissue, nerves and/or mucosal tissue), or disease relapse. The remaining cases were provisionally classified as tumors of uncertain biologic behavior. A number of morphologic parameters were then evaluated under light microscopy and univariate and multivariate analyses were adopted for this study.

RESULTSHistologic findings correlated with evidences of the following morphologic parameters were considered in accord with the criteria of the malignant behavior: mitotic count>or=10 per 50 high-power fields (P<0.01), muscle infiltration (P<0.01), coagulative necrosis (P<0.01), perivascular growth pattern (P=0.005) and remarkable nuclear atypia (P=0.014). Basing on the above criterion, 485 cases were re-classified as "malignant" and 355 cases "non-malignant". Follow-up data showed that the five-year disease-free survival and overall survival in the "non-malignant" group were 99.3% and 100% respectively, in contrast to 43.9% and 59.7% respectively in the "malignant" group (P<0.01).

CONCLUSIONSThe set of clinicopathologic parameters is useful in predicting the malignant behavior of GIST and prognosis.