Secretion of Pancreatic Polypeptide in Patients with Pancreatic Endocrine Tumors

Pancreatic polypeptide is often secreted by pancreatic endocrine tumors and is considered a marker for such tumors. To investigate the diagnostic value of this marker, we studied 323 patients with proved pancreatic endocrine tumors. We found plasma concentrations of pancreatic polypeptide to be elevated (more than 300 pmol per liter) in 144 patients (diagnostic sensitivity, 45 percent). However, plasma levels of pancreatic polypeptide can also be elevated in the absence of a pancreatic tumor. To ascertain whether the administration of atropine could distinguish between normal and tumor-associated polypeptide secretion, we studied 30 patients with pancreatic tumors and high plasma levels of pancreatic polypeptide, 18 patients without tumors who had elevated levels of pancreatic polypeptide, and eight normal controls. Polypeptide levels In the 18 patients without tumors were substantially lower than in the 30 patients with tumors. Atropine (1 mg intramuscularly) did not suppress polypeptide levels in patients with tumors, but did suppress plasma levels by more than 50 percent in all subjects without tumors. Thus, although its diagnostic sensitivity is low, pancreatic polypeptide appears to be a useful adjunctive marker of many pancreatic endocrine tumors, and the atropine suppression test can be used to distinguish normal from tumor-related secretion of the polypeptide. Identification of the type of pancreatic endocrine tumor still requires measurement of the hormone that is specific for the tumor. (N Engl J Med 1986; 315:287–91.), PANCREATIC polypeptide is the hormonal product of a distinct type of endocrine cell that is a major component of the islets of Langerhans.^1,2 It is composed of 36 amino acids, but its physiologic function has not been clearly defined. The cells that produce it are often present in pancreatic endocrine tumors, and patients with such tumors may have massively elevated plasma concentrations of pancreatic polypeptide.^{3 4 5 6 7} Overall, about 50 percent of patients with pancreatic endocrine tumors have elevated plasma levels of pancreatic polypeptide.³ Measurement of plasma pancreatic polypeptide appears to be of value both in the diagnosis of these tumors and….