NENs are classified by the World Health Organisation (WHO) 2017 grading system according to Ki-67 or mitotic index and cellular differentiation; Grade 1 tumours are well-differentiated with a Ki-67 < 3%, Grade 2 tumours are well-differentiated with a Ki-67 of 3–20% and Grade 3 neoplasms are further divided into well-differentiated tumours with a Ki-67 > 20% or poorly differentiated neuroendocrine carcinomas (NECs) [6]. The gene discussed is MKI67; the disease is neoplasm.