Giant Rectal Gastrointestinal Stromal Tumor Successfully Resected after Neoajuvant Therapy with Imatinib Mesylate: Report of a Case

Abstract

The case reported here concerns a 78-years-old man who was referred for additional screening of the left side wall of the rectum during an examination for prostate cancer. Magnetic resonance imaging (MRI) revealed a low rectal tumor measuring 77mm in diameter, and a biopsy specimen was positive for CD34 and c-kit. Based on these findings, the tumor was diagnosed as a rectal GIST. The boundaries between the prostate gland or left muscle obturatorius internus and the tumor were unclear. It was considered an invasion. We decided to treat the case with neoajuvant therapy using imatinib mesylate (IM) to reduce the tumorʼs size. He took IM at a daily dose of 400mg. After 11 months, MRI revealed a decrease of the maximal diameter of the tumor to 37mm (a 52％ reduction) and it had not invaded further. Fourteen months after the initial diagnosis, laparoscopic abdominoperineal resection was performed. Although 4 years and 5 months have passed since the surgery, obvious signs of recurrence have yet to be observed.

The present case suggests that neoajuvant therapy using IM is useful for advanced rectal GIST.