Evaluation of alterations in tumor tissue of gastrointestinal stromal tumor (GIST) in computed tomography following treatment with imatinib

Background: The aim of this study was to evaluate the alterations in the neoplastic tissue of GIST following Imatinib treatment. Material/Methods: CT studies of 14 patients with inoperable primary tumors and 56 patients with metastatic and recurrent disease after chemotherapy were analyzed retrospectively. The following alterations in features of primary and secondary tumors were analyzed: dimension, degree and type of contrast enhancement, outlines of lesions, presence of intratumoral bleeding, presence of calcifications. Results: In the analyzed group of primary, metastatic and recurrent tumors after treatment with Imatinib in most cases a decrease in size and contrast enhancement were observed; the outlines of lesions became well circumscribed. Following the treatment, the number of tumors enhancing inhomogeneously decreased. In primary tumors the percentage of calcifications increased, whereas in metastatic tumors calcifications were observed only after treatment. There was no bleeding found within primary tumors after treatment. In metastatic disease, increased percentage of tumors with transient intratumoral bleeding was observed. There were also some unconventional CT images following treatment, such as: cystic transformation of lesions, enlargement of lesions, appearing of new lesions suggesting progression of the disease, stationary dimensions of lesions during local progression of the disease, simultaneous decrease and increase in size of metastatic lesions or appearance of new ones. Conclusions: Right from the start of Imatinib therapy in inoperable and disseminated GIST patients, specific CT images, not seen during conventional cytotoxic chemotherapy, were observed.