Histopathologically, most NENs are well-differentiated (WD) tumours grade 1 (G1, Ki67 ≤2%), grade 2 (G2, Ki67 3–20%) or grade 3 (G3, Ki67 >20%), whereas a small fraction are defined as poorly differentiated (PD) neuroendocrine small-cell or large-cell carcinoma (NEC) with a Ki67 >20% (5, 6). Here, MKI67 is linked to neoplasm.