MKI67 and neuroendocrine carcinoma: According to the eighth edition of the AJCC/UICC (American Joint Committee on Cancer/Union for International Cancer Control) recommendations, the ESMO (European Society for Medical Oncology) guidelines, and the 2022 WHO (World Health Organization) classification, NETs are defined as NET G1 (Ki-67 < 3%), NET G2 (Ki-67 3–20%), NET G3 (Ki-67 > 20%, usually between 21–55%) and NEC (neuroendocrine carcinoma, Ki-67 usually > 55%) (i.e., low-differentiated carcinomas with a highly aggressive clinical course) [6,7,8].