Insulinomas are tumors of the pancreatic beta cells, either benign or malignant, that lead to hyperfunctioning of these cells. These cells are unresponsive to the normal negative feedback mechanisms (hypoglycemia) that normally turn off insulin production. This results in dysregulated and excessive production of insulin.
It is also reported that there is a regional difference in the occurrence of insulinoma in ferrets, where the highest reported number of cases is in the United States (where most owners are feeding commercial dry kibble diets), and less reported in Europe and Asia. It is debated whether it is a genetic, nutritional, or environmental difference, although most data points to a genetic and nutritional difference.