[Value of scintigraphic explorations by radiomarkers others than iodine radioisotope in differentiated thyroid cancer]. / Intérêt des explorations scintigraphiques par des radiotraceurs autres que l'iode radioactif dans le cancer thyroïdien différencié.

ABSTRACT

Radioiodine scintigraphy is the gold standard exploration for imaging metastases of differentiated thyroid cancer and enables the decision of therapy with 131 radioactive iodine to be made. However, other approaches may be of use for diagnosis when there is no visible uptake after the administration of 131I, while elevated thyroblobulin levels suggest the presence of metastatic tissue in one third of metastatic patients. In order to detect recurrences or metastases, in conjunction with conventional imaging techniques (cervical and hepatic ultrasonography, lung CT scan..), other scintigraphic explorations with various radiopharmaceutics may be used, although none of them has any specificity towards thyroid cancer. Tl201 and MIBI which are used as perfusion tracers for myocardial explorations, are also used for detection of various tumors and for metastatic thyroid cancer. The performances of both radiopharmaceutics in imaging metastases are differently evaluated between investigators with a sensitivity ranging from 45 to 94% while the specificity varies less (82-97%). 18-Fluoro-deoxyglucose is retained in malignant tissue depending on the grade of malignancy. It has been shown to accumulate in thyroid cancer and metastases. Its detection by whole body PETscan represents a limitation for use which will be modified by new techniques. 111In-octreotide which binds to somatostatin receptors located on tumor cell membranes is able to show thyroid cancer metastases in some instances. We report on the very preliminary results of these combined scintigraphic approaches, performed in a limited number of patients who had no radioiodine uptake and elevated Tg levels, in order to determine the most appropriate exploration in terms of performance and cost.