Among well-differentiated gastroenteropancreatic neuroendocrine tumors, DLL3 expression was identified in 5/235 (2%) of grade 1-2 and 25/66 (40%) grade 3 (G3) tumors, most commonly G3 pancreatic NETs (PanNETs; 22/52, 43%), with univariate analysis revealing increased mortality risk among patients with DLL3-positive advanced G3 PanNETs (hazard ratio 3.27 [95% CI, 1.09 to 9.78]). This evidence concerns the gene DLL3 and pancreatic neuroendocrine tumor.