MKI67 and neuroendocrine carcinoma: According to the World Health Organization (WHO) classification, NENs are subdivided into well-differentiated neuroendocrine tumors (NETs), graded as G1 (Ki-67 <3% or <2 mitoses/10 high-power fields[HPF]), G2 (Ki-67 3–20% or 2–20 mitoses/10 HPF), and G3 (Ki-67 >20% with well-differentiated morphology), and poorly differentiated neuroendocrine carcinomas (NECs), which are inherently high-grade (G3) with small- or large-cell morphology.