Oral malignant gastrointestinal neuroectodermal tumour with junctional component mimicking mucosal melanoma.

Malignant gastrointestinal neuroectodermal tumour (GNET) is a recently characterised rare and aggressive tumour that typically arises in association with the small intestine of adults. We present a novel case of this entity and expand the spectrum of its reported morphological features. The patient was a 5-year-old female, the youngest reported patient affected by the condition, and presented with extra-abdominal disease. The histopathological features included the presence of a junctional component of the palatal tumour, which mimicked mucosal melanoma, a feature that has not been previously reported in GNET. Whole genome and RNA sequencing was performed that demonstrated the EWSR1-ATF1 translocation characteristic of GNET. Knowledge of this entity and its features, together with careful morphological assessment supplemented by judicious immunohistochemical and molecular studies should enable the correct diagnosis to be established.