Pancreatic polypeptide-producing tumours are rare and are not associated with a clinical syndrome, despite the fact that they are functional and secrete high levels of pancreatic polypeptide in the blood.

The tumours are usually single and benign, although a few have metastasized to the liver.

Pancreatic polypeptide is also secreted by other islet cell tumours in addition to their specific hormones, especially after stimulation by a meal, and it has been suggested that it may be a useful adjunct marker to detect islet cell tumours.

Neoplasms of the Endocrine Tumours ; Normal Islets of Langerhans ; The Apud Concept ; Islet Cell Tumours ; Alpha Cell Tumours ; Beta Cell Tumours (Insulinomas) ; Somatostatinoma ; VIPomas ; Enterochromaffin Cell (Carcinoid) Tumours ;Multiple Endocrine Neoplasia (MEN) Syndrome.  

PP-producing tumors are mostly located in the pancreas and may present as three pathologic lesions: pure PP-omas, mixed tumors with minor PP cell population, and PP-cell hyperplasia. These tumors are among the most common multiple adenomas frequently found in patients with multiple endocrine neoplasia type 1. Hypersecretion and high circulating levels of PP are frequently found. They are symptomless but may be useful for the identification of the pancreatic tumors. Numerous types of extrapancreatic endocrine tumors are able to synthesize and secrete PP. They occur mostly but not exclusively in the gastrointestinal tract, particularly in the rectum. The inactivation of the MEN 1 gene at 11q13 appears to be involved in the development of pancreatic but not of rectal PP-producing tumors.

Pancreatic polypeptide hyperplasia causing watery diarrhea syndrome: a case report.Can J Surg. 1999 Feb;42(1):55-8.

Neuroendocrine tumours of the pancreas can secrete numerous peptides, leading to various recognizable clinical syndromes. The secretion of pancreatic polypeptide has been used as a marker for neuroendocrine tumours but is considered to be a biologically inert peptide. A 37-year-old woman had watery diarrhea syndrome from pancreatic polypeptide hyperplasia. Only 2 other reported cases in the literature have described pancreatic polypeptide hyperplasia; however, this is the first reported case in which the patient was successfully treated by surgical resection, with a 2-year follow-up. This report and review of the literature illustrate that pancreatic polypeptide hypersecretion may present as a clinical endocrinopathy.

Pancreatic polypeptide-producing tumors. Silent lesions of the pancreas? Arch of Surg. Vol. 119 No. 5, May 1984.

Eight patients with pancreatic polypeptide (PP)-producing islet cell tumors and one patient with pseudo-PP-producing tumors were examined. Their age range was 20 to 74 years. Clinical features included abdominal pain in four patients, weight loss in four patients, diarrhea in two patients, gastrointestinal bleeding in two patients, and jaundice in one patient. The range of the basal serum level of PP was 394 to 35,100 pg/mL. In two patients the PP-producing tumors were associated with multiple endocrine neoplasia. Two patients had diffuse hepatic metastases at the time of diagnosis and four patients had disease limited to the pancreas. Pancreaticoduodenectomy and 80% pancreatectomy were performed in four and two patients, respectively. Immunohistochemical staining was positive for PP and neuron-specific enolase in all cases and was negative for other peptides except in one specimen with microadenomatosis. Patients who underwent curative resection are asymptomatic with normal serum levels of PP.