DETECTION OF OCCULT GASTRINOMAS WITH IODINE 125-LABELED LANREOTIDE AND INTRAOPERATIVE GAMMA-DETECTION

Background. Surgical exploration for gastrinoma has a high failure rat e because of small primary tumors and occult metastasis. Despite exten sive preoperative and intraoperative tumor localization, only 30% to 4 0% of patients with gastrinoma are cured by surgery. Two patients with unlocalized gastrinomas were studied with intraoperative gamma detect ion of an iodine 125-labeled somatostatin analog, lanreotide, to local ize their tumors. Methods. Both patients were challenged before operat ion with 100 mu g of octreotide acetate, and both had circulating gast rin levels suppressed by greater than 50%. Iodine 125-labeled lanreoti de (100 to 150 mu Ci) was injected during exploration, and an intraope rative gamma detector was used to detect tumor binding of the analog. Results. In patient 1 a single source of increased counts was discover ed in a retroduodenal lymph node, which was excised; no other tissue w as removed. Histologic study of this node failed to demonstrate tumor; however, the patient's gastrin level was normal (63 pg/ml) 4 months a fter operation. In patient 2 five areas of increased counts were disco vered and excised. Three of these five areas had visible tumor on micr oscopic examination. Three months after the operation the patient's fa sting gastrin level was 103 pg/ml. Conclusion. Intraoperative gamma de tection of radiolabeled peptides may allow the localization of occult tumors that contain specific peptide receptors.