OBJECTIVETo investigate the clinical characteristics, diagnosis and treatment as well as prognostic factors of the giant gastrointestinal stromal tumor (GIST).

METHODSClinical data of 235 patients with high risk GIST treated in the Union Hospital, Tongi Medical College, Huazhong University of Science and Technology between January 2005 and July 2015 were retrospectively analyzed. Patients were divided into giant GIST group (diameter equal to or larger than 10 cm, 119 cases) and high risk group (diameter less than 10 cm, 116 cases) according to tumor size. Clinical characteristics and prognosis of two groups were compared and the clinical features of giant GIST were summarized. Multivariate analysis was performed to evaluate the prognostic factors of giant GIST with Cox regression model.

RESULTSOf the 119 patients with giant GIST, which accounted for 50.6%(119/235) of all the high risk patients, there were 63 male and 56 female patients with a median age of 53(20-82) years. Primary giant GIST of 43(36.1%) located in the stomach, of 39(32.8%) in the small intestine, 5(4.2%) in the colon and rectum, and of 32 (26.9%) outside the gastrointestinal tract (mesentery, retroperitoneum, abdominal cavity, etc) and pelvic. Compared to high risk group, age of onset was younger [ratio of ≤50 years, 44.5%(53/119) vs. 31.9%(37/116), P = 0.046] and incidence of outside the gastrointestinal tract was significantly higher [26.9%(32/119) vs. 9.5%(11/116), P=0.000] in giant GIST group. All the giant GIST patients underwent surgical resection, including 115 cases(96.6%) of R0 resection, 3 cases(2.5%) of R1 resection and 1 case(0.9%) of R2 resection, besides, 32 cases(26.9%) underwent expanded resection (namely, underwent lymphadenectomy or combined organ resection simultaneously). Thirty-nine giant GIST cases(32.8%)accepted imatinib 400 mg/d for targeted therapy after operations, which was not significantly different with high risk group (46 cases, 39.6%, P=0.232). Relapse and metastasis occurred in 8 cases in giant GIST group. The 1-, 3-, 5-year overall survival rates of giant GIST group were 94.5%, 89.3%, 79.4% respectively and of high risk group were 99.1%, 92.9%, 85.1% respectively, and no significant difference was found (P=0.788). The 1-, 3-, 5-year recurrence-free survival rates of giant GIST group were 93.6%, 85.1%, 72.8% respectively and of high risk group were 99.1%, 91.7%, 84.2% respectively, and no significant difference was found as well (P=0.932). Multivariate analysis revealed that gender (P=0.047, RR=0.383, 95%CI:0.149-0.987), mitotic count (P=0.001, RR=0.216, 95%CI:0.087-0.538) and targeted therapy(P=0.019, RR=5.719, 95%CI:1.324-24.695) were prognostic risk factors of overall survival (OS), moreover, tumor size (P=0.024, RR=0.368, 95%CI:0.155-0.875) and mitotic count(P=0.007, RR=0.357, 95%CI:0.169-0.755) were prognostic risk factors of RFS.

CONCLUSIONSGiant GIST is not unusual in GIST and more likely occurs outside gastrointestinal tract. Complete surgical excision combined with targeted therapy can improve the prognosis significantly. The prognosis of giant GIST and common high risk GIST is similar. Mitotic count is the most important prognostic factor.