Comparison of ⁶⁸Ga-prostate-specific membrane antigen, ⁶⁸Ga-dotatate and ¹⁸F-FDG in metastatic radioiodine refractory hurthle cell variant of follicular thyroid carcinoma: a case report

Hurthle cell carcinomas (HCCs) are rare differentiated thyroid neoplasms of follicular cell origin which have a greater tendency to metastasise to distant sites and a higher mortality rate. The majority of HCCs are refractory to radioiodine therapy and are difficult to treat as they also respond poorly to chemoradiotherapy. Molecular therapies such as tyrosine kinase inhibitors can be used with some success however they are limited by high cost and side effect profile. Some radioiodine refractory (RAIR) thyroid cancers demonstrate prostate specific membrane antigen (PSMA) expression and radionuclide therapy with ¹⁷⁷Lutetium PSMA has been used as treatment in this setting. ¹⁷⁷Lu-labelled somatostatin analogues have also been used with mixed results likely due to variable somatostatin receptor-2 expression. Case Presentation: We present a case of a 51 year old female with metastatic RAIR, Hurthle cell variant of follicular thyroid cancer which showed poor Gallium-68 (Ga-68) PSMA avidity but high SSTR-2 expression on ⁶⁸Ga-DOTATATE PET/CT. Uptake with ⁶⁸Ga-DOTATATE PET/CT was similar to that of ¹⁸F-FDG PET/CT which makes peptide receptor radionuclide therapy (PRRNT) with ¹⁷⁷Lu-DOTATATE a therapeutic option for this patient. The patient subsequently received targeted radionuclide therapy with ¹⁷⁷Lu-DOTATATE, and the scan performed after the first cycle of ¹⁷⁷Lu-DOTATATE demonstrated significant uptake and retention in most of the lesions. This case report demonstrates the poorer radioiodine and PSMA avidity of Hurthle cell thyroid carcinoma in comparison to ⁶⁸Ga-DOTATATE and emphasises ¹⁷⁷Lu-DOTATATE as appropriate choice of ligand to be considered for radionuclide therapy in this histological subtype of thyroid cancer. (author)