neuroendocrine tumor of the appendix, well differentiated, low or intermediate grade (MONDO_0015066, a Monarch Disease Ontology entry) is a well differentiated, low or intermediate grade tumor with neuroendocrine differentiation that arises from the appendix. Also known as: NEN of appendix, appendiceal NEN, appendiceal neuroendocrine neoplasm, appendiceal neuroendocrine tumor, appendiceal neuroendocrine tumour, appendix NET, appendix neuroendocrine tumor, appendix neuroendocrine tumour.