MKI67 and neuroendocrine carcinoma: The guidelines of the European and American societies regarding the frequency of follow-up imaging for NEN offer varied recommendations, typically suggesting follow-up intervals of 6–12 months in patients with R0/R1-resected NET G1 and NET G2 with low Ki-67 (< 5%), or every 2 to 3 months for tumors with high proliferation rates, such as NET G2 (Ki-67 > 5%) and NEC/NET G3.