MKI67 and neuroendocrine carcinoma: According to the WHO classification from 2019, they are grouped on the basis of their proliferation index into well differentiated grade 1 (G1, Ki-67 < 3%), grade 2 (G2, Ki-67 3–20%) and grade 3 (G3, Ki-67 > 20%) neuroendocrine tumours (NETs) and the rare, poorly differentiated G3 neuroendocrine carcinomas (NEC, Ki-67 > 20%) [2].