Secondary resistance to imatinib mesylate 70 months after initiation of therapy in a patient with a metastatic gastric gastrointestinal stromal tumor.

It is unknown how long the risk of developing secondary resistance to imatinib persists in patients with gastrointestinal stromal tumors (GISTs). Here we report a case of a patient with a metastatic gastric GIST who developed secondary resistance to imatinib 70 months after initiation of imatinib therapy. A 62-year-old woman with a gastric GIST underwent total gastrectomy with pancreaticosplenectomy. Immunohistochemistry revealed a KIT-positive GIST. The mitotic index of the tumor was 13/50 high-power fields, indicating a high-risk malignancy. After surgery, the patient developed a solitary liver metastasis and underwent right hepatic lobectomy. Four months later, a metastatic tumor was found at the left adrenal gland, and imatinib therapy was initiated in December 2004. Imatinib therapy led to marked tumor shrinkage and complete clinical remission in the patient. However, in October 2010, computed tomography scans revealed a peritoneal metastasis in the ileocecal area. The tumor progression was clinically determined to be due to the development of secondary resistance to imatinib, and the patient's treatment was switched to sunitinib. This case illustrates secondary resistance to imatinib can develop even after a sustained and marked treatment response. Long-term therapy and close monitoring are recommended for the management of patients with metastatic GISTs.