Ampulla of Vater Neuroendocrine Tumor G3

**Semantic type:** Neoplastic Process

**Definition:** A well-differentiated, high-grade neuroendocrine neoplasm that arises from the ampulla of Vater and the periampullary region. The mitotic count is more than 20 per 2 mm2 and/or the Ki-67 index is more than 20%.