Peptide Receptor Radionuclide Therapy with Lu-177-DOTATATE and Monitoring with Somatostatin Receptor PET/CT in Patients with Advanced Differentiated Thyroid Carcinoma.

PURPOSE: Peptide receptor radionuclide therapy (PRRT) with Lu-177-DOTATATE is an established treatment option for neuroendocrine tumors (NETs) and has been extended to other somatostatin receptor (SSTR)-expressing tumors. We aimed to determine its efficacy and safety profile in patients with advanced radioiodine-refractory differentiated thyroid carcinoma (DTC).

METHODS

Seven radioiodine-refractory DTC patients undergoing at least two cycles of PRRT were included. Patients were subdivided into continuous treatment (defined as sequential application of PRRT; 5/7 (71.4%)) vs. discontinuous treatment (with at least one-year PRRT-free interval; 2/7 (28.6%)). Baseline SSTR PET was analyzed to determine patients' eligibility for PRRT. Response was assessed by tumor control as defined by stable (± 30.0%) or decreasing (≥ 30.0%) total tumor volume (PET-derived TTV), thyroglobulin (Tg) and RECIST 1.1 criteria.

RESULTS

SSTR PET showed discernible high uptake (maximum standardized uptake values, 10.4 ± 8.6) in metastases, in particular in the skeleton. Continuous PRRT showed variable tumor control (stable disease / response; TTV: 3/5 (60.0%); Tg: 2/5 (40.0%); RECIST 1.1: 3/5 (60.0%)). All patients undergoing discontinuous PRRT exhibited concordant stable disease upon first follow-up and renewed tumor control upon reinitiating PRRT (RECIST 1.1; decreasing TTV and Tg levels). No Common Terminology Criteria for Adverse Events (CTCAE) Grade 3-5 events occured in both groups.

CONCLUSION

In advanced radioiodine-refractory DTC, PRRT may be beneficial even after treatment interruptions, without major side effects. Given the small cohort and retrospective design, further prospective studies are needed to optimize PRRT strategies in DTC, in particular in a rechallenge scenario.