Detection of occult gastrinomas with iodine 125-labeled lanreotide and intraoperative gamma detection

Background. Surgical exploration for gastrinoma has a high failure rate because of small primary tumors and occult metastasis. Despite extensive preoperative and Intraoperative tumor localization, only 30% to 40% of patients with gastrinoma are cured by surgery. Two patients with unlocalized gastrinomas were studied with Intraoperative gamma detection of an iodine 125-labeled somatostatin analog, lanreotide, to localize their tumors. Methods. Both patients were challenged before operation with 100 μg of octreotide acetate, and both had circulating gastrin levels suppressed by greater than 50%. Iodine 125-labeled lanreotide (100 to 150 μCi) was injected during exploration, and an Intraoperative gamma detector was used to detect tumor binding of the analog. Results. In patient 1 a single source of increased counts was discovered in a retroduodenal lymph node, which was excised, no other tissue was removed. Histologic study of this node failed to demonstrate tumor; however, the patient's gastrin level was normal (63 pg/ml) 4 months after operation. In patient 2 five areas of increased counts were discovered and excised. Three of these five areas had visible tumor on microscopic examination. Three months after operation the patient's fasting gastrin level was 103 pg/ml. Conclusions. Intraoperative gamma detection of radiolabeled peptides may allow the localization of occult tumors that contain specific peptide receptors.