MKI67 and neuroendocrine carcinoma: Based on pathological characteristics, PanNENs had previously been classified into grade 1 pancreatic neuroendocrine tumours (PanNETs) (well-differentiated morphology with Ki-67 < 3%); grade 2 PanNETs (well-differentiated morphology with Ki-67 3–20%) and grade 3 neuroendocrine carcinoma (Ki-67 > 20%, regardless of morphology).