Grade 3 Neuroendocrine Tumor (G3NET): An Unusual Tumor With A Histochemical Surprise

Given the rare occurrence and the indolent course of Neuroendocrine tumors (NETs), few epidemiological studies exist on these cancers. A small but interesting subset of these tumors are G3- Neuroendocrine Tumors. Grade 3 Neuroendocrine tumors (or G3-NETs) are unique in their intermediate prognosis. These grade discordant tumors lie in between high-grade poorly differentiated neuroendocrine carcinomas and grade 2 well-differentiated NETs, which have a worse and better prognosis than this rare entity, respectively. In this case report, we present a case of Grade 3 NET with an unusually high Ki67 index, diagnosed upon biopsy of metastasis visualized on imaging. Additionally, we review existing literature for characteristics, immunohistochemical markers, prognosis, and treatment modalities for the same.