According to the World Health Organization (WHO) classification, NENs are classified, based on morphology and proliferation index, into well-differentiated neuroendocrine tumors (NETs G1, Ki67 < 3%; NET G2, Ki67 3–20%; NET G3, Ki67 > 20%) and poorly differentiated neuroendocrine carcinomas (NECs, always G3) [3]. Here, MKI67 is linked to neuroendocrine carcinoma.