MKI67 and neuroendocrine carcinoma: Following these criteria, GEP-NENs are classified as follows: grade (G) 1-NET (Ki-67 < 3%; well-differentiated morphology), G2-NET (Ki-67 3–20%; well-differentiated morphology), G3-NET (Ki-67 > 20%; well-differentiated morphology), and G3-NEC (Ki-67 > 20%; poorly-differentiated morphology).