According to the 2022 WHO Classification of Endocrine and Neuroendocrine Neoplasms (NENs), these tumors are broadly divided into neuroendocrine tumors (NETs), neuroendocrine carcinomas (NECs), and mixed neuroendocrine–non-neuroendocrine neoplasms (MiNENs), based on morphological features, mitotic activity, and Ki-67 proliferation index (1–3). The gene discussed is MKI67; the disease is neuroendocrine carcinoma.