Indolent Gastrointestinal Neuroectodermal Tumor (GNET) of the Colon: A New Entity?

With less than 50 reported cases, gastrointestinal neuroectodermal tumor (GNET) is a rare malignant neoplasm. Here we report an unusual case of GNET with indolent clinical behavior. The patient is a 59-year-old Caucasian man whose 2 cm sigmoid colon mass did not increase significantly in size during a 10-year surveillance colonoscopy. This mass was recently resected due to change in bowel habits. H&E sections revealed a polypoid, low-grade spindle cell neoplasm, arising from the submucosa and infiltrating the muscularis propria. Negative CD117 and DOG-1 stains excluded a diagnosis of gastrointestinal stromal tumor (GIST). The tumor cells were positive for vimentin, S-100, synaptophysin, and CD56. Pertinent negative stains included Melan-A, HMB-45, smooth muscle actin, CD34, and cytokeratin. Electronmicroscopy showed no obvious sign of differentiation. A presumptive diagnosis of GNET was made. FISH for rearrangement of the EWSR1 gene was, however, negative. There was no evidence of metastatic disease at the time of surgery. One year after surgical removal of this tumor, the patient is asymptomatic. We propose that a subset of GNET may follow an indolent clinical course.