NEW RADIOPHARMACEUTICALS FOR EXPLORATION OF DIFFERENTIATED THYROID-CANCER

Radioiodine scintigraphy is the gold standard exploration for imaging metastases of differentiated thyroid cancer and enables the decision o f therapy with 131 radioactive iodine to be made. However, other appro aches may be of use for diagnosis when there is no visible uptake afte r the administration of 131I, while elevated thyroblobulin levels sugg est the presence of metastatic tissue in one third of metastatic patie nts. In order to detect recurrences or metastases, in conjuction with conventional imaging techniques (cervical and hepatic ultrasonography, lung CT scan..), other scintigraphic explorations with various radiop harmaceutics may be used, although none of them has any specificity to wards thyroid cancer. Tl201 and MIBI which are used as perfusion trace rs for myocardial explorations, are also used for detection of various tumors and for metastatic thyroid cancer The performances of both rad iopharmaceutics in imaging metastases are differently evaluated betwee n investigators with a sensitivity ranging from 45 to 94 % while the s pecificity varies less (82-97 %). 18-Fluoro-deoxyglucose is retained i n malignant tissue depending on the grade of malignancy. It has been s hown to accumulate in thyroid cancer and metastases. Its detection by whole body PETscan represents a limitation for use which will be modif ied by new techniques. 111In-octreotide which binds to somatostatin re ceptors located on tumor cell membranes is able to show thyroid cancer metastases in some instances. We report on the very preliminary resul ts of these combined scintigraphic approaches, performed in a limited number of patients who had no radioiodine uptake and elevated Tg level s, in order to determine the most appropriate exploration in terms of performance and cost.