MKI67 and neuroendocrine carcinoma: Furthermore, NET/NEC are graded into three levels based on different definitions of proliferation using the mitotic count and/or the Ki-67 index: Grade 1 (G1), mitotic count < 2 per 10 high-power fields (HPF) and/or Ki-67 ≤ 2%; Grade 2 (G2), mitotic count 2–20 per 10 HPF and/or Ki-67 3 to 20%; Grade 3 (G3), mitotic count > 20 per 10 HPF and/or Ki-67 > 20% [8, 14].