Insulinoma (functional islet cell tumor) is the most common neuroendocrine tumor in domestic species. See discussions of insulinoma Functional Islet Cell Tumors in Small Animals Islet cell tumors are the most common cause of hypoglycemia in older dogs. Clinical signs vary but often consist of weakness, ataxia, collapse and seizures. Diagnosis is by documenting hypoglycemia... read more and gastrinoma Gastrin-secreting Islet Cell Tumors in Dogs and Cats Gastrinomas are functional tumors of the pa s that secrete the hormone gastrin. They are rare but have been reported in people, dogs, and a cat. Hypersecretion of gastrin in people results in... read more .