Established rare syndromes are caused by vasoactive intestinal peptide (VIP) secretion or somatostatin (somatostatinoma), ACTH (ACTHoma), serotonin (carcinoid syndrome), or PTHrpP (PTHrpP-oma, causing hypercalcemia) secretion. Here, VIP is linked to ACTH-producing pituitary gland adenoma.