The WHO 2010 classification divided GEP-NEN according to the Ki67 index (and mitotic count) into neuroendocrine tumours (NET) grade 1 (Ki67 < 2%), NET grade 2 (Ki67 3–20%) and neuroendocrine carcinomas (NEC) grade 3 (Ki67 > 20%). Here, MKI67 is linked to neuroendocrine carcinoma.