According to the proliferation index (Ki67%), mitotic count, and histology, GEP NENs are classified as well differentiated NETs (grade 1; Ki67% < 3%, grade 2; Ki67% 3–20%, and grade 3; Ki67% > 20%), or poorly differentiated small-cell or large-cell neuroendocrine carcinoma (NEC; Ki67% > 20%) [15]. This evidence concerns the gene MKI67 and large cell neuroendocrine carcinoma.