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. DiscussionGNET is a rare visceral spindle cell neoplasm, characterized by neural differentiation in the absence of melanocytic features [6,7,10]. The differential diagnosis for GNET is broad and ranges from GIST through smooth muscle tumors (e.g., low-grade leiomyosarcoma), perivascular epithelioid cell tumors (so-called PE Comas), monophasic synovial sarcoma and schwannoma to metastatic tumors. In our case, GIST was excluded based on the negative immunohistochemical stains for CD117 and DOG1. Melanocytic differentiation markers (Melan-A and HMB-45) were also negative, thereby ruling out PEComa and melanoma. The negativity of smooth muscle actin and desmin further

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