CT appearances of responsive gastrointestinal stromal tumors (GISTs) after imatinib mesylate treatment

Abstract

Background : Gastrointestinal stromal tumors (GISTs) have their specific receptor that allows the use of specific target drug. CT scan is the imaging technique of choice to evaluate the response of the tumor. There are some conflicts about CT parameter such as size and density that confuse radiologists in the evaluation of the tumor response.

Objective : Our objective is to evaluate CT appearances in patients with GISTs who have response after imatinib treatment by combination of RECIST criteria and density, vascularity, solid nodule and cystic change of the tumor.

Design : Retrospective study

Setting : King Chulalongkorn Memorial Hospital, Thai Red Cross Society.

Materials and Methods : Sixty-five tumors from 14 patients were 33 intrahepatic and 32 extrahepatic lesions. All patients underwent contrast-enhanced MDCT scan in both pre-and post treatment periods. The axial images of CT portovenous phase with 8-mm slice thickness were reviewed by the author and one experienced gastrointestinal radiologist, with consensus.

Results : Significant decrease in size and density of overall tumors were noted. The extrahepatic lesions had statistically significant decrease in both size and density than intrahepatic lesions. On pre-treatment images, solid nodules within the lesions were found in 18 lesions (27.7%), mainly in extrahepatic lesions while tumor vessels were found in 7 extrahepatic lesions (10.8%). There were new cystic-like lesions in the liver of 2 patients on post-treatment images. No new solid mass was seen after treatment.

Conclusion : Our data supports other studies on the response of GISTs to imatinib treatment. We suggest that in case of mismatch between size and density, size may not be reliable factor. Density, vascularity, solid nodule and cystic change may complement to each other in evaluation of response to treatment in addition to size. Extrahepatic lesions display more definite response in terms of size and density when compared to intrahepatic lesions.