MKI67 and neuroendocrine neoplasm: The World Health Organization (WHO) currently recognizes 4 main histopathological subgroups with strong prognostic implications: G1 (Ki-67 < 3%), G2 (Ki-67 3–20%), and well-differentiated G3 (Ki-67 > 20%) neuroendocrine tumor (NET), which are progressively more aggressive, and poorly differentiated neuroendocrine carcinoma (NEC), which is the most aggressive subset.