Biochemical diagnosis of gastroenteropancreatic endocrine tumors

Functioning gastroenteropancreatic endocrine tumors produce and secrete different substances that can be detected in the plasma and cause hormone-related syndromes. Symptoms such as diarrhea associated either with typical skin rash or peptic ulcer disease may be suggestive of the presence of intestinal carcinoid or gastrinoma. Other clinical manifestations such as severe hypoglycemia, diabetes, necrolytic erythema and gallbladder disease may also indicate an endocrine tumor. Sometimes, patients present no, or just vague, symptoms such as dyspepsia or abdominal pain and nonfunctioning endocrine tumors in these patients can be found incidentally during diagnostic imaging procedures or at operation. Usually, the diagnosis is established by the measurement of the specific tumor marker in the plasma and, sometimes, in the urine. In some cases, normal basal hormone levels are observed even in the presence of typical symptoms. Therefore, stimulatory tests such as the secretin test for gastrinomas are required to establish the diagnosis. General markers for the diagnosis of gastroenteropancreatic endocrine tumors are also available. Among these, chromogranin A has proved to be of great value for diagnosing nonfunctioning tumors and is considered the most sensitive general marker. The availability of both specific and general markers as well as stimulatory tests may enable the clinician to diagnose functioning gastroenteropancreatic endocrine tumors at an early stage and to recognize nonfunctioning tumors.