MKI67 and neuroendocrine carcinoma: Histologically, these are divided into three grades on the basis of clinical behavior, histology, and proliferation rate: Well differentiated, G1, low grade when the Ki67 index is less than 2%, Intermediate group G2 with Ki67 2-20% and mitosis also 2-20%/10HPF, and poorly differentiated or G3, high grade neuroendocrine carcinoma with mitosis >20/10HPF and Ki67 more than 20%.