The Size and Number is Not Everything to Evaluate the Tumor Response

Gastrointestinal stromal tumors are the most common mesenchymal tumors of the gastrointestinal tract. Contrast-enhanced computed tomography is the most commonly used for evaluating response to treatment. Targeted therapies may cause some changes in tumor structure. Reduced lesion vascularity, cavitations, and intratumoral hemorrhage are some changes in patients after imatinib therapy, even without any size reduction. Paradoxically, a transient increase in size may be seen in some cases due to cystic change and intratumoral hemorrhage. Alternative tumor response criteria were developed by Choi et al. in gastrointestinal stromal tumor. They showed that not only the tumor size but also the tumor density are important in evaluating the response. In the present study, we report a 67-year old man who had been diagnosed with the gastrointestinal stromal tumor and treated with imatinib. After 3 months of imatinib treatment, liver lesions reported progression in response assessment.