INSM1 and acinar cell carcinoma: In fact, in an analysis of cell block samples, INSM1 displayed 100% sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for differentiating NET from non-NET pancreatic tumors, as SPN (solid pseudopapillary neoplasm), ACC (acinar cell carcinoma), and PDAC (pancreatic ductal adenocarcinoma) samples were always INSM1 negative (unlike SYP which was positive for SPN), making it a useful marker for excluding possible non-NET diagnoses [54,55].