We present a case of gastrointestinal stromal tumor (GIST) of the rectum.
A 55-year-old man was admitted to the hospital because of a rectal tumor detected at a medical checkup in April 2003. Digital examination revealed an about 3-cm sized elastic-hard mass with a smooth surface, locating about 3cm oral from the anal verge. Colonoscopic examination showed a submucosal tumor encircling about 1/4 of the lumer in the lower rectum which had the smooth surface without ulcer. A transanal core needle biopsy was performed. HE staining showed a solid growth of spindle-shaped cells, and immunohistochemically the tumor cells were positive for CD34 but negative for SMA and S100. GIST was thus diagnosed. Considering that lymph node dissection was unnecessary and the anal function was able to be preserved, we performed a transsacral partial resection of the rectum. No local recurrence or distant metastasis has occurred, as of 20 months after the operation.