Peptide receptor radionuclide therapy (PRRT) of treatment-refractory metastatic thyroid cancer using Yttrium-90 and Lutetium-177 labeled somatostatin analogs: Toxicity, response and survival analysis

Objectives Evaluation of short and long term toxicity and therapeutic efficacy (response and survival) of PRRT in radioiodine-nonavid/therapy refractory thyroid cancer patients.

Methods 15 iodine-nonavid/radioiodine therapy refractory thyroid cancer patients (mean age 60 yrs, M:F 7:8) were treated with PRRT using Y-90 and/or Lu-177 SMS analogs (DOTA-TATE/-TOC or -NOC). All patients were heavily pretreated and presented with progressive disease in the follow-up. The dose range per cycle for Y-90 was 2500-5000 MBq, and 3500 - 7500 MBq for Lu-177. Primary histology: follicular cancer (n=4), medullary thyroid cancer (n=7), Hurthle cell carcinoma (n=3), and mixed carcinoma (n=1). Ga-68 Somatostatin Receptor PET/CT was used to determine the somatostatin receptor density in the metastastes and in recurrent tumor lesions and to assess treatment response. PRRT was performed under strict nephroprotection with amino acid infusions. Hematological profiles and renal function (GFR and TER) were regularly monitored after PRRT.

Results Only mild, reversible hematological or renal toxicity was observed (maximum grade 1). Response assessment in 11 patients treated with 2 or more (maximum 5) cycles of PRRT showed partial remission in 2 patients (18%), and disease stabilization in 4 (36%) patients. 1 patient showed a mixed response whereas in 4 patients (37%) disease progressed further. Mean survival (Kaplan-Meier analysis) after first PRRT was 4.2 years, median progression free survival was 25 months.

Conclusions In iodine-nonavid or radioiodine therapy refractory thyroid cancer patients, PRRT is an effective therapeutic option with minimal toxicity, good response rates and significant survival benefits