A term that refers to the staging of an ampulla of Vater neuroendocrine tumor according to the American Joint Committee on Cancer, 8th edition. This staging system applies to well-differentiated neuroendocrine tumors of the ampulla of Vater. Carcinomas of the ampulla of Vater, including high-grade (grade 3), poorly differentiated neuroendocrine carcinomas are not included in this staging system. (from AJCC 8th Ed.) [from NCI]