In the present study the prognostic value of the immunohistochemical markers p53, SSTR-2a and CgA were thoroughly investigated in a large cohort of 163 GEP-NEN patients with a Ki67-index > 20%, including well-differentiated NET G3 and poorly differentiated NEC according to the recent WHO 2019 classification. This evidence concerns the gene MKI67 and neuroendocrine carcinoma.