99mTc-HYNIC Octreotide and 68Ga-DOTATATE in differentiated thyroid cancer patients with raised thyroglobulin levels and negative 131I whole-body scans: Head-to-head comparison

Objectives Thyroid cancer is the most common endocrine tumor and its incidence is increasing. Nuclear medicine plays an important role in the clinical management of the disease. It has been described the use of 99mTc labeled somatostatin analogues for thyroid cancer patient evaluation after surgery and iodine treatment in those who persist with high thyroglobulin levels and a negative iodine whole body scan. The aim of our work was to perform an intrapatient comparison of 68Ga DOTATATE PET-CT with 99mTc HYNIC Octreotide scans in ten patients of this special population of thyroid cancer patients and follow up them for one year.

Methods 68Ga DOTATATE PET/CT examinations were performed to 12 patients bearing diferentiated thyroid cancer (9 papillary and 3 follicular) post-thyroidectomized with raised thyroglobulins (1,5 to 63,64 ng-ml; mean 9,38 ng-ml), negative antithyroglobulins and negative whole body scans (10 women, age 27-53 yo, 2 men, age 49-70) that already had a positive 99mTc HYNIC Octreotide scintigraphy. Studies were performed after obtaining informed consent and our Ethics Committee approval.

Results 99mTc HYNIC Octreotide scintigraphy showed focal (n=9), diffuse (n=3) and focal-diffuse (n=4) uptake in the neck. 68Ga DOTATATE PET studies showed concordant matches with 99mTc HYNIC Octreotide scans in only three patients. One of these three patients went into surgery and had confirmation of a thyroid cancer node relapse. We did not find significant changes in their thyroglobulin levels, whole body iodine scans and 99mTc HYNIC Octreotide scans after one year of the initial evaluation.

Conclusions These results may reflect the different somatostatin receptor expression in thyroid cancer associated to different affinities of these two radiolabeled somatostatin analogues and the rather slow progression of these tumors. This information may path the way to new insights to in vivo molecular understanding of somatostatin receptor expression in thyroid cancer.

Research Support Comisión Sectorial Investigación Científica (CSIC)