COMBINED USE OF IN-111-DTPA-D-PHE-1-OCTREOTIDE (OCT) AND I-123 VASOACTIVE-INTESTINAL-PEPTIDE (VIP) IN THE LOCALIZATION DIAGNOSIS OF MEDULLARY-THYROID CARCINOMA (MTC)

Although serum calcitonin and CEA are sensitive indicators for the pre sence of medullary thyroid carcinoma (MTC), the localization of tumor sites may be very difficult. In an approach to localize MTC lesions we performed comparative in vivo studies in 12 patients with primary MTC and in 4 patients with suspected recurrent MTC using I-123-VIP (150 M Bq/1 mu g) and In-111-DTPA-D-Phe-1-octreotide (In-111-OCT; 150 MBq/1 m u g) Despite elevated calcitonin values in all patients with suspected recurrent or meta-static lesions, both ultrasound and computed tomogr aphy (CT) were unable to localize a tumor site. In-111-OCT localized t he primary tumor in the thyroid gland in 7 of 11 patients (63.5%). In 2 of 4 patients (50%) with suspected recurrent MTC, pathological uptak e of In-111-OCT in the mediastinum or liver was demonstrable. In none of the 11 patients did I-123-VIP receptor scanning indicate primary, r ecurrent, or metastatic tumor lesions. In vitro binding studies showed an absence of high-affinity VIP receptors in MTC tissue, whereas high -affinity In-111-OCT receptors were present in 4 of 6, and low-affinit y I-123-VIP as well as In-111-OCT receptors were present in 6 of 6 MTC tissue samples. We conclude that somatostatin receptor scanning using In-111-OCT may visualize primary MTC, but it has only a low sensitivi ty in the detection of recurrent disease. The I-123-VIP-receptor scan is not helpful in the localization diagnosis of primary or recurrent M TC.