CT is commonly used to assess therapeutic response in patients with GISTs. CT enables characterization of primary and recurrent tumors. In the past, the treatment response has been classically quantified using only a decrease in size as the main criterion inhibitor manufacture for tumor response[10]. Recent studies have shown a cyst-like appearance with no further decrease in size is inconsistent with therapeutic response[11�C13]. The purpose of this study was to evaluate and characterize the patterns of disease progression of metastatic or unresectable GIST treated with imatinib mesylate. In addition, the study sought to determine the prognostic significance associated with disease progression. MATERIALS AND METHODS The study was conducted under the approval of the Institutional Review Board and Ethics Committee of Ramathibodi Hospital Faculty of Medicine, Bangkok, Thailand.

Seventeen consecutive patients with metastatic and unresectable GISTs diagnosed histopathologically as positive for CD117 were included in this retrospective review. All patients had a period of imatinib treatment during October 2002 to October 2006. Patients received a starting dose of 400 mg/d imatinib mesylate orally. In the event of disease progression, an increase in daily dosage to 800 mg was allowed. In cases of side effects, the dose was decreased to 300 mg/d. In cases of clinical non-response or death, the treatment was terminated. Our patients included 13 men and four women, aged 36-69 (mean 53) years. The primary tumor sites were the stomach (eight patients), small bowel (six), rectum (two) and retroperitoneum (one patient).

At enrollment, 10 patients had initial metastatic disease, three had recurrent disease, three had no free surgical margin, and one had unresectable advanced disease. Sixty-two lesions (38 in the liver, nine in the mesentery, six in the pararectal region, three in the stomach, two in the peritoneum, two in the lymph nodes, one in the retroperitoneum, and one in bone) were evaluated on the basis of the Response Evaluation Criteria in Solid Tumors (RECIST) criteria for each organ and body compartment invaded by the tumor. Inclusion criteria were as follows: (1) all lesions > 1.0 cm in the longest diameter; and (2) lesions ranging from 0.5 to 1.0 cm in the longest diameter, with no more than five lesions. Exclusion criteria were: (1) lesions < 0.

5 cm in the longest diameter; and (2) lesions which were difficult to follow up due to changing location (small bowel and mesentery), or having partial volume. We retrospectively reviewed the medical Batimastat records and radiological features of each patient. Imaging techniques Each patient underwent baseline CT before treatment (with the exception of patients who underwent scans at another hospital before treatment). Follow-up studies consisted of CT at 1-mo intervals for up to 6 mo after imatinib mesylate treatment.