They are classified according to the WHO classification into well-differentiated neuroendocrine tumors (NET) (either G1, G2, or G3 grading based on Ki-67 index and mitotic count), poorly differentiated and highly aggressive neuroendocrine carcinoma (NEC), and mixed neuroendocrine–non-neuroendocrine neoplasm (MiNEN) [3]. The gene discussed is MKI67; the disease is neuroendocrine neoplasm.