Corticotropinoma is an islet cell tumour that secretes both low- and high- molecular weight ACTH.

It may also simultaneously secrete gastrin, insulin, corticotrophin-releasing hormone, melanocyte-stimulating hormone, and other peptides and amines.

The symptoms reflect high blood levels of cortisol from an ACTH-induced adrenocortical hyperplasia.

The diagnosis is established by the documentation of high levels of ACTH and the failure to respond to the suppressive effects of dexamethasone.