The triad of diabetes, gallstones and steatorrhea is associated with -

The somatostatinoma syndrome is due to an neuroendocrine tumour (NET) that secretes excessive amounts of somatostatin, which causes a distinct syndrome characterized by diabetes mellitus, gallbladder disease, diarrhea, and steatorrhea. The mean age is 51 years. Somatostatinomas occur primarily in the pancreas and small intestine. Reference : page 570 Harrison's Principles of Internal Medicine 19th edition