[Case of primary retroperitoneal GIST (gastrointestinal stromal tumor) with rapid progression].

A 69-year-old man complaining of left abdominal pain was referred from a private clinic for retroperitoneal masses that were discovered on abdominal ultrasound in November 2010. CT scan showed retroperitoneal masses, located above the left kidney, measuring 10 cm. Para-aortic lymph nodes were swelling. We performed open biopsy to make the diagnosis in December 2010. The diagnosis was primary retroperitoneal GIST (gastrointestinal stromal tumor). We started imatinib 400 mg/day according to the Japan GIST guideline in January 2011. However the tumor pogressed rapidly, after 1 month the patient died.