Malignant gastrointestinal neuroectodermal tumor of the colon showing DOG1 positivity and S100 negativity: A case report.

Malignant gastrointestinal neuroectodermal tumor (MGNET) is a rare and highly aggressive malignancy originating in the gastrointestinal tract. It resembles various gastrointestinal mesenchymal tumors in appearance and microscopic morphology. While typical immunohistochemistry aids diagnosis, abnormal immunophenotypes can complicate it. We report a case of MGNET in the transverse colon in a 37-year-old man. Immunohistochemical results showed DOG1 positivity and S100 negativity, mimicking CD117-negative/DOG1-positive gastrointestinal stromal tumors (GIST). Fluorescence in situ hybridization (FISH) revealed EWSR1 gene rearrangement, and next-generation sequencing (NGS)-based RNA fusion gene detection identified EWSR1::ATF1 fusion, supporting the diagnosis of MGNET. We will discuss the abnormal immunophenotype and differential diagnosis of MGNET, reviewing relevant literature.