Lutetium-177 peptide receptor radionuclide therapy of de-differentiated thyroid cancer

Introduction: Well-differentiated thyroid cancer when originates from thyroid follicular epithelium and retains its biological characteristics. This allows for it to be treated with radioactive iodine therapy (RAI). About 5% of patients develop metastatic thyroid disease, which is refractory to RAI. Lutetium-177-labelled peptide receptor radionuclide therapy (PRRT) was explored as an alternative option. Methods: Sixty-three-year-old female with follicular thyroid cancer post-thyroidectomy more than 10 years ago, presented with right hip pain because of a surgically irresectable mass in the right hemi-pelvis with lytic destruction of the right hip involving the lesser trochanter, acetabulum, ilium and pubic rami. A diagnostic iodine-123 (I-123) whole-body scan (WBS) revealed uptake in the thyroid bed (thyroid remnant tissue), focal uptake in the left cervical lymph node and heterogenous uptake in the right hemi-pelvis, most intense over the right hip lesser trochanter. She received two cycles of I-131 therapy in 2019 at 150 mCi and 2021 at 200 mCi. Post 2nd cycle of I-131 therapy, the post-therapy no longer showed uptake in the right pelvic mass with exception of a focus in the lesser trochanter. A dedifferentiated thyroid carcinoma was suspected. F18-Fluoro-D-glucose (F18-FDG) positron emission tomography/computed tomography (PET/CT) scan revealed a destructive, locally infiltrative lesion in the right hemipelvis with abnormal, intense and homogenous uptake. A Ga-68-DOTATATE PET/CT scan demonstrated somatostatin receptor expression at a Krennig score 4 in the mass, congruent to the FDG uptake, with a mildly avid right inguinal lymph node. Post-workup for PRRT, she received a total of cycles of Lu-177-DOTATATE therapy. Results: Post three cycles, her ECOG score improved from 3 to 1 and her post-therapy scans showed a reduction in the size and uptake of the pelvic mass. The post-therapy scan following her 4th cycle revealed stable disease. The Ga-68 DOTATATE was repeated as per protocol, at 6 months after her fourth cycle. This scan revealed progression of the lesion in right hemipelvis with regard to intensity and size. Discussion and conclusion: Treatment options for dedifferentiated thyroid cancer refractory to I-131 are limited and tend to show a suboptimal response. Peptide receptor radionuclide therapy with beta-emitting and alpha- emitting radionuclides serves as an alternative option in thyroid cancer lesions expressing somatostatin receptors. The relatively short range of Lu-177 may be a factor which results in a slow response given the size of the lesion of the above patient, and tandem treatment with Y-90 PRRT may need to be considered. (authors)