Clinicopathological features and prognosis of small gastrointestinal stromal tumors outside the stomach

The aim of the present study was to assess the clinicopathological features and prognostic factors of primary small gastrointestinal stromal tumors (GISTs) outside the stomach. The clinical data, clinicopathological features and prognostic factors of 20 patients with a pathologically-confirmed diagnosis of non-gastric GIST that were treated at Liaoning Cancer Hospital & Institute between July 2006 and December 2013 were retrospectively analyzed. In total, 15 patients were male and 5 were female, with a median age of 58 years (range, 44-82 years). A change in bowel habits was the original symptom of rectal small GISTs in 6 out of 8 patients, while patients with small GISTs in other locations demonstrated no overt symptoms and the lesions were detected by systematic examinations of other diseases or abdominal surgical procedures performed on other organs. In total, 19 patients out of the total 20 patients underwent surgery, and 1 patient with rectal GIST received continuous oral imatinib mesylate (400 mg once a day) instead of undergoing surgery. The mean diameter of tumors was 1.55±0.54 cm (range, 0.3-2.0 cm) and the median was 1.70 cm. The pathomorphology of the lesions was mainly spindle cell, and immunohistochemistry revealed the expression rate of cluster of differentiation (CD)117, CD34 and discovered on GIST-1 were 85, 80 and 70%. According to the mitosis index, small rectal GISTs were more frequent compared with other positions (P<0.05), while the frequency of small GISTs >1 cm in size was not significantly different from the frequency of small GISTs ≤1 cm in size (P=0.995). All 20 patients were followed up, with a median follow-up duration of 49.5 months (range, 10.5-94.4 months). At the end of the follow-up period, tumor recurrence occurred in 5 patients and 1 patient succumbed following progression. According to the analysis of the tumor sites, the RFS time of patients with small rectal GISTs was significantly different than the RFS time in patients with small GISTs in other positions. The clinical symptoms of non-gastric small GISTs were not evident and were challenging to detect. Small GISTs, regardless of size, possessed malignant potential and once detected, GISTs should be surgically resected. Lesions located in the rectum demonstrated an increased degree of malignancy and were more likely to recur. The tumor size and Ki67 index could not be considered as prognostic factors of non-gastric small GISTs.