Extended octreotide suppression test to determine hormone responsiveness of multiple type I gastric carcinoid tumors

A 70-year-old man was found to have at least 12 type I gastric carcinoids and microcarcinoidosis. We performed an extended octreotide suppression test to determine if the tumors were gastrin-dependent and would likely regress after antrectomy. He was given an octreotide infusion at 12.5-25 mcg/h for 86 hr followed by depot octreotide 20 mg intramuscularly every four weeks for eight months. Fasting serum gastrin and chromogranin A levels were measured, and endoscopy with biopsies was performed before and after the infusion and at five months and eight months. Total RNA was extracted for quantitation of histidine decarboxylase mRNA using real-time PCR. Fasting serum gastrin decreased from 306 pg/ml pretreatment to 31 pg/ml at the end of infusion and 115 pg/ml at eight months. Chromogranin A decreased from four to six times the upper limit of normal to normal. Tissue histidine decarboxylase mRNA decreased 50-fold. At eight months, only a few diminutive nodules were present on endoscopy. These results demonstrated that the carcinoid tumors in this patient were under neuroendocrine control and were expected to respond to antrectomy.