Imaging of Gastrointestinal Stromal Tumors: From Diagnosis to Evaluation of Therapeutic Response

Once considered an obscure tumor entity with poor prognosis, gastrointestinal stromal tumors (GISTs) are nowadays recognized as the most common mesenchymal tumors of the alimentary tract. GISTs differ from other mesenchymal neoplasms at pathology since 90% of them exhibit strong immunohistochemical staining for KIT, a tyrosinase kinase growth factor receptor. In the early 2000s, the ability of imatinib mesylate, a tyrosine kinase inhibitor, to inhibit KIT established a new paradigm for cancer treatment. A reduction in lesion size may not be observed or may appear many months after therapy; thus, tumor response criteria alternative to the Response Evaluation Criteria in Solid Tumors were developed. This review highlights the role of imaging in the detection, characterization, preoperative staging, postoperative assessment, therapy-response evaluation and treatment-related toxicities. All this information is crucial in optimizing patient management. Contrast-enhanced computed tomography is the most commonly used modality for staging the disease and assessing treatment response, whereas positron-emission tomography adds valuable functional information. Magnetic resonance imaging (MRI) may also be useful, especially in ano-rectal GISTs. Diffusion-weighted MRI may provide promising indicators of tumor response to targeted molecular therapy. Radiologists and oncologists should be aware of all these issues related to GISTs, since multidisciplinary teams gathering different expertise are usually needed to properly treat patients with GISTs.