Neuroendocrine tumours are a general term for a large group of tumours, ranging from inert, slow-growing benign tumours to low-grade malignant tumours, to highly metastatic, significantly malignant tumours.
In general, tumours graded as G1 and G2 are less malignant and G3 is more malignant, and classification as neuroendocrine carcinoma is a malignant tumour of high malignancy.