[A Case of Gastric GIST with Pathological Complete Response Achieved by Long-Term Chemotherapy with Imatinib Mesylate].

A 78-year-old woman was diagnosed with a gastrointestinal stromal tumor(GIST)of the stomach, gradually increasing from 5 years prior. The tumor was suspected to invade the pancreatic body tail and spleen, as observed with computed tomography. Because the patient refused to undergo resection, we administered imatinib mesylate for 6 years. Since early rectal cancer was revealed, the patient was referred for resection and underwent laparoscopic low anterior resection and partial gastrectomy. Histopathologically, the tumor was replaced by tissues with myxomatous changes, and no viable tumor cells were detected. This was a rare case of GIST, resected after long-term chemotherapy by imatinib mesylate, and pathological complete response was achieved.