Signature: © Pol J Radiol, 2011; 76(3): 38-48 Received: 2010.12.06 Accepted: 2011.05.16 R E V I E W A R T I C L E Characteristics of computed tomography imaging of gastrointestinal stromal tumor (GIST) and related diagnostic problems Agnieszka Werewka-Maczuga1, Tomasz Osiński2, Robert Chrzan1, Magda Buczek1, Andrzej Urbanik1 1 Radiology Department, Jagiellonian University Medical College, Cracow, Poland 2 Opole Oncology Center, Opole, Poland Author’s address: Agnieszka Werewka-Maczuga, Department of Diagnostic Imaging, Kopernika 19 Str., 31-501 Cracow, Poland, e-mail: awerewka@mp.pl Summary In this article, authors presented several characteristic features of Gastrointestinal Stromal Tumors (GISTs), which may lead to diagnostic errors and unexpected difficulties during interpretation of CT images. In case of GIST, one may encounter problems at every level of diagnostics and treatment response monitoring, especially after introduction of modern molecular targeting therapies. RECIST scale criteria, used until now for evaluation of response to treatment in solid tumors are based merely on the size of the tumor and turned out to be inadequate after introduction of treatment with new molecular target drugs such as Imatinib. Key words: GIST • CT • imaging PDF file: http://www.polradiol.com/fulltxt.php?ICID=881951 GIST (gastrointestinal stromal tumor) is currently the most commonly diagnosed sarcoma of the gastrointestinal tract and its incidence is still increasing. Relatively recently, i.e. in 1998, this neoplasm was distinguished from a group of other gastrointestinal tract sarcomas after prof. Hirota had discovered a mutation in cKIT [1] protooncogene, which is crucial for the development of this tumor. Since then, the expression of KIT protein (CD 117 antigen) with tyro- sine kinase activity on the surface of the tumor cells has become the main diagnostic criterion. GIST is resistant to a standard chemo- and radiotherapy. The only curative treatment is radical surgical excision. The effects of treatment of inoperative or metastatic GISTs were, until recently, very poor (median survival after recur- rence was 9–20 months). However, in recent years there have appeared radical changes in the therapy of advanced tumors due to the discovery and implementation of treat- ment with tyrosine-kinase inhibitors. GIST has been the first solid tumor treated with an advanced molecular target- ing therapy since 2001, when Imatinib [2,3] was introduced. 38 Detection of the primary tumor and neoplastic metastases, as well as monitoring of treatment response with radiologi- cal imaging sometimes present a challenge for the radiol- ogist because of the diversity of pictures of the disease at every clinical stage. Especially the evaluation of response to molecular targeting therapy in computed tomography (CT) may present problems because radiological images usually differ from those in conventional chemotherapy. Incorrect interpretation of these images due to a strict application of the criteria of response to therapy based merely on chang- es in tumor size may result in early discontinuation of an effective drug and premature death of a patient. Difficulties may appear already during diagnostics of the primary tumor. Primary GIST tumors are most often dis- covered in endoscopic studies as intramural tumors with a frequent characteristic ulceration at the top. However, lesions may be found both inside as well as on the outside of every part of the gastrointestinal tract and also within the omentum and mesentery, without any connection with the gastrointestinal tube, which poses problems or pre- cludes endoscopic detection of the tumor [4]. Figures 1–3 illustrate GIST lesions of various growth patterns.