Objective:We aimed to evaluate the clinicopathologic characteristics,immunohistochemical expression and prognostic factors of patents with primary gastrointestinal stromal tumors (GISTs).Methods:Data from 2,570 consecutive GIST patients from four medical centers in China (January 2001-December 2015) were reviewed.Survival curves were constructed by the Kaplan-Meier method,and Cox regression models were used to identify independent prognostic factors.Results:Of the included patients,1,375 (53.5％) were male,and the patient age range was 18 to 95 (median,58) years.The tumors were mostly found in the stomach (64.5％),small intestine (25.1％) and colorectal region (5.1％).At the time of diagnosis,the median tumor size was 4.0 (range:0.1-55.0) cm,and the median mitotic index per 50 high power fields (HPFs) was 3 (range:0-254).Of the 2,168 resected patients,2,009 (92.7％) received curative resection.According to the modified National Institutes of Health (NIH) classification,21.9％,28.9％,14.1％ and 35.1％ were very low-,low-,intermediate-and high-risk tumors,respectively.The rate of positivity was 96.4％ for c-Kit,87.1％ for CD34,96.9％ for delay of germination 1 (DOG-l),8.0％ for S-100,31.0％ for smooth muscle actin (SMA) and 5.1％ for desmin.However,the prognostic value of each was limited.Multivariate analysis showed that age,tumor size,mitotic index,tumor site,occurrence of curative resection and postoperative imatinib were independent prognostic factors.Furthermore,we found that high-risk patients benefited significantly from postoperative imatinib (P＜0.001),whereas intermediate-risk patients did not (P=0.954).Conclusions:Age,tumor size,mitotic index,tumor site,occurrence of curative resection and postoperative imatinib were independent prognostic factors in patients with GISTs.Moreover,determining whether intermediate-risk patients can benefit from adjuvant imafinib would be of considerable interest in future studies.