Endocrine tumors of the pancreas associated with elevated urinary serotonin excretion

A review is presented of four cases of pancreatic endocrine tumors associated with elevated levels of blood serotonin or urine 5 hydroxyindoleacetic acid (5 HIAA). Clinical, light and electron microscopic observations are presented. Of the four cases associated with elevated levels of blood serotonin or urine 5 HIAA, three were indistinguishable pathologically from carcinoid or islet cell tumors. A fourth case was morphologically identical to oat cell carcinoma of the lung. In one tumor ultrastructural study and comparison with the pulmonary carcinoid tumor aided in more precise classification that was possible by light microscopic techniques alone.