MKI67 and neuroendocrine carcinoma: NENs are pathologically classified depending on cells’ morphology and differentiation (Ki-67 and the mitotic count) into well-differentiated tumors (NETs) (graded as NET G1: Ki-67 < 3% or mitotic count per 10 high-power fields < 2; NET G2: Ki-67 with 3–20% or 2–20 mitoses; NET G3 Ki-67 > 20% or > 20 mitoses) [1,2] and poorly differentiated neuroendocrine carcinoma (NEC, Ki-67 > 20%).