The special aims of this study were to investigate (1) the prevalence of NET G3 regarding origin and metastasis; (2) the characterization of NET G3 regarding Ki67 index and p53, Rb1, and SST2 expression; (3) the value of immunohistochemistry in the differential diagnosis of NET G3 versus NEC; and (4) the agreement between referral diagnosis and final diagnosis. The gene discussed is TP53; the disease is neuroendocrine carcinoma.