The well-differentiated neuroendocrine tumors (NETs) are divided according to their proliferation into grade 1 (Ki-67 index ≤ 2%) grade 2 (Ki-67 index 3–20%), grade 3 (Ki-67 index > 20%), and the grade 3 tumors are further divided into low-differentiated grade 3 neuroendocrine cancers (NECs). The gene discussed is MKI67; the disease is neuroendocrine carcinoma.