Nuclear staining for the neuroendocrine transcription factor Insulinoma-associated protein-1 (INSM1) has very high sensitivity and specificity (99 and 96% respectively) for GEP-NET, and 100% positive and negative predictive value for differentiating pancreatic NET from other pancreatic differentials including ductal adenocarcinoma, solid pseudopapillary neoplasm and acinar cell carcinoma [36–38]. The gene discussed is INSM1; the disease is acinar cell carcinoma.