MKI67 and neuroendocrine carcinoma: G1 NETs require a Ki-67 index of <3% and a mitotic rate of <2 mitosis/2 mm2, G2 is defined by a Ki-67 index of 3–20% or a mitotic rate of 2–20/2 mm2, and G3 NETs and NEC have a Ki-67 index of >20% or a mitotic rate of >20 mitosis/2 mm2.