MKI67 and carcinoid tumor: According to The World Health Organization (WHO) classification (2010), NETs are classed as NET G1 (carcinoid, mitotic count <2 per 10 high power fields (HPF) and/or ≤2% Ki67 index), NET G2 (mitotic count 2–20 per 10 HPF and/or 3–20% Ki67 index), NET G3 (neuroendocrine carcinoma, mitotic count >20 per 10 HPF and/or >20% Ki67 index), and mixed adenoneuroendocrine carcinoma (MANEC) (1,2).