Abstract
We present a case of a gastrointestinal stromal tumor (GIST) of the rectum in a 63-year-old man who had visited our hospital complaining of pain on voiding. Digital examination revealed a hard mass, the surface of which was smooth, fixed at the anterior wall of the rectum, 4cm oral from the anal verge. CT and MRI showed an Inhomogeneous mass 10cm in size, occuping the small pelvic cavity. A transrectal needle biopsy was performed. Immunohistochemistry findings showed the tumor cells were strongly stained with CD34, weakly with c-kit gene product, but were not stained with S-100 protein nor smooth muscle actin. From these findings, a diagnosis of a GIST (uncommitted type) was made, and an abdominoperineal excision was performed. Macroscopically the tumor was 14×10×8cm in size, showing exoluminal growth from the anterior wall of the rectum. Immunohistochemical staining of the resected specimen was the same as that of the needle biopsy specimen. Successful reduction of c-kit-positive recurrent GIST by STI571, which was produced to treat chronic myelocytic leukemia, has been reported. Immunohistochemical staining of the specimen obtained by transrectal needle biopsy is useful to determine whether neoadjuvant therapy by STI571 is effective.
