There are two classes of gastrinoma defined by the groups of people affected:
Sporadic - making up 75% of cases, when tumours arise as isolated lesions in otherwise healthy individuals. The cause of the sporadic type is not fully understood. Excess alcohol intake has been implicated in some individuals.
Familial - making up the remaining 25% cases. This is where gastrinoma occurs as part of the Multiple Endocrine Neoplasia syndrome type 1 (MEN-1), where several distinct but related endocrine conditions occur together. The familial type is genetic, where a tendency to develop the tumour and MEN-1 is inherited. Isolation of the most important genes hasrecently been achieved.
Gastrinomas are found in up to 2% of people with recurrent ulcers that are not responding to treatment, and in 0.1% patients with a duodenal ulcer.