We report two cases of postoperative recurrence of gastrointestinal stromal 
tumor (GIST) treated by the tyrosine kinase inhibitor imatinib mesylate (IM), 
and discuss some important items. Case 1: This 63-year-old Japanese man received 
a partial gastrectomy for leiomyosarcoma in 1993. Partial hepatectomy and 
proximal gastrectomy were performed for liver metastasis and local recurrence in 
2001. However, 5 months after surgery, a CT scan showed multiple tumors in the 
liver, lung and thyroid. The patient was treated with 300 mg of IM once daily 
with transient grade 2 neutropenia and intestinal bleeding. Though the response 
to treatment was SD-PR initially, a CT scan 15 months after initial treatment 
demonstrated the regrowth of the tumor in his liver. Case 2: A 63-year-old 
Japanese woman was treated with 200 mg of IM once daily for multiple liver 
metastases after gastrectomy for GIST with grade 3 neutropenia and edema of 
legs. The response to treatment was SD, and continued for 12 months. IM is the 
treatment of choice for unresectable recurrence of GIST. However, some problems 
remained. Both basic and clinical research is necessary to increase the 
therapeutic efficacy of IM.