Grade 1 (G1), G2, and G3 tumors with the Ki-67 indices of ≤ 3%, 3-20%, and 20-50% are the well-differentiated ones, and G3 tumors with a Ki-67 index of > 50% are classified as poorly differentiated neuroendocrine carcinomas (2). Here, MKI67 is linked to neuroendocrine carcinoma.