Biopsy of a liver mass demonstrated a high-grade NEN with well-differentiated nested morphology, oncocytic cytoplasm, uniform nuclei, a mitotic count of 23 per 2 mm2, and Ki-67 index of 45%, suggestive of G3 NET, but IHC demonstrated aberrant p53 positivity and loss of Rb expression, suggestive of NEC (Supplemental Fig. 1). The gene discussed is MKI67; the disease is neuroendocrine carcinoma.