MKI67 and neuroendocrine carcinoma: According to WHO classification of digestive system tumors, NENs might be highly or moderately differentiated called neuroendocrine tumors (NETs G1 or G2 with Ki 67 index below 20%) and poorly differentiated with Ki67 over 20% (NET G3 with still organoid histology or NEC (neuroendocrine carcinoma) without organoid histology (4).