A VIPoma is a tumour that secretes large amounts of vasoactive intestinal polypeptide (VIP) and peptide histidine methionine (PHM). The hormone VIP is widely distributed in the body, acting as a local neurotransmitter and a gut regulatory hormone. VIP acts to encourage bowel movement producing the watery diarrhoea characteristic of VIPoma. It is also a smooth muscle relaxant. PHM mimics the effects of VIP by acting on the same receptor, although its effects are less pronounced.
In adults they occur mainly in the islet cells of the head or tail of the pancreas. They occur less commonly in children, and in such cases they arise in the sympathetic chain (ganglioneuroblastomas). Between 50 and 75% of VIPomas are malignant. They were first described by Verner and Morrison in 1958, leading to the clinical features sometimes being known as Verner-Morrison Syndrome.
The estimated incidence is 1 in 10 million each year, and of those 70% tend to occur in females. The average age of incidence is 47 years, however this also includes a significant portion of young children with ganglioneuroblastomas.