OBJECTIVETo investigate the clinicopathological and molecular genetic characteristics of gastrointestinal stromal tumor (GISTs) with significant cystic changes, and to assess their biological behavior.

METHODSClinicopathological features of 7 patients with cystic GISTs treated at the Zhongshan Hospital of Fudan University from February 2005 to January 2010 were summarized retrospectively. The mutations status of c-kit and PDGFR-α were analyzed.

RESULTSThere were 2 males and 5 females aged from 46 to 76 years old. Primary site of GISTs included stomach(n=4), duodenum(n=1), and small intestinal(n=2). Tumor size ranged from 6 to 16 cm with obviously cystic changes. Tumor cells were found in the solid components under microscope, of which epithelioid cell type were found in 4 case and spindle cell type in 3 cases. The mitotic figures were no more than 3/50 HPF in all the patients. According to the NIH criteria, 4 were high-risk and 3 were low-risk. Based on morphological characteristics, 3 cases were as borderline tumor, 3 moderate-risk, and 1 moderate-risk. Gene mutation of exon 11 of c-kit were identified in 3 cases. During the follow up ranging from 9 to 80 months, all the 7 patients had cancer-free survival.

CONCLUSIONThe biological behavior of cystic GIST is indolent with a low risk of malignancy and favorable prognosis.