MKI67 and neoplasm: The 2010 tumor grade classification of the World Health Organization (WHO) divides panNET into three prognostic groups based on the proliferation index assessed through the expression of the nuclear antigen Ki67, with Ki67 < 3% classified as low-grade panNET (G1), Ki67 3–20% classified as intermediate-grade panNET (G2), and Ki67 > 20% classified as high-grade neuroendocrine carcinoma (NEC) (G3).8–11