Gastrointestinal stromal tumor: New nodule-within-a-mass pattern of recurrence after partial response to imatinib mesylate

PURPOSE: To investigate a new pattern of tumor recurrence observed at imaging in patients with metastatic gastrointestinal stromal tumor (GIST) after initial partial reponse to imatinib mesylate. MATERIALS AND METHODS: Ninety-two patients with metastatic GIST who underwent treatment in a clinical trial with oral imatinib mesylate were followed up for 29 months. An institutional review board-approved protocol was used. The study complied with the Health Insurance Portability and Accountability Act, and written informed consent was obtained from all patients. Images of the chest, abdomen, and pelvis, acquired with computed tomography (CT), positron emission tomography (PET), and, in some cases, magnetic resonance imaging, were evaluated for treatment response and disease recurrence. Thirty-nine patients (29 men, 10 women; age range, 18-84 years; mean, 49.2 years) had recurrent disease after an initial variable period of response (range, 2-24 months; median, 14.4 months). Initial response was determined with findings of decreased uptake of fluorine 18 fluorodeoxyglucose at PET, shrinkage of tumor, and decreased attenuation at CT. Images were evaluated for disease recurrence by two experienced radiologists who were blinded to each other's interpretation but not to clinical details. Final reading was performed by consensus. RESULTS: A nodule within a mass was seen in 21 of 39 patients (in intrahepatic tumor [n = 8], extrahepatic tumor [n = 10], or both intra- and extrahepatic tumors [n = 3]) and was the first sign of disease progression in 17 of 21 patients. Other patterns of recurrence included new site of disease (n = 7), regrowth of preexistent lesion (n = 20), and mixed (more than one) pattern (n = 9). Disease progression was verified at needle biopsy (n = 16), follow-up imaging (n = 14), and/or surgical resection (n = 9). CONCLUSION: A nodule within a mass is an important sign of recurrent GIST, but measurements of overall tumor size may not enable detection of such nodules. RSNA, 2005