Discordant Primary Resistance to Imatinib Mesylate in the Same Individual and Splenic Involvement in Recurring Gastric Gastrointestinal Stromal Tumors: Assessment by Fluorodeoxyglucose-Positron Emission Tomography/Computed Tomography.

Discordant primary resistance and response of the metastatic lesions in the same individual coupled with splenic involvement in gastrointestinal stromal tumors (GISTs) are relatively uncommon. We herein report such a case of recurring GIST of the stomach that presented with the involvement of spleen with F-fluorodeoxyglucose positron emission tomography-computed tomography (FDG PET-CT) imaging documentation. Ultrasonography-guided fine needle aspiration cytology from the splenic and paravesical lesions demonstrated metastatic spindle cell tumor consistent with diagnosis of metastasis from GIST of the stomach. The splenic and the paravesical lesions appeared resistant to the conventional 400 mg of imatinib mesylate, while most other abdominopelvic metastatic lesions demonstrated good metabolic response on FDG-PET/CT, with the noteworthy findings of interlesional heterogeneity of the metastatic lesions in terms of differential primary response in the same individual.