Endocrine Abstracts

Purpose: Although the majority of differentiated thyroid cancer (DTC) patients have favorable outcome, approximately up to 20% of them may develop metastatic and/or locoregional disease persistence. One-third of those patients may not respond to the treatment with radioiodine (RAI refractory DTC, RAI-R DTC). There are few reports of real-life experience concerning the clinical course and the treatment modalities that have been used in patients with RAI-R DTC.

Methods: We conducted a retrospective study focusing on the clinical characteristics at diagnosis, the location and time interval of the appearance of metastatic lesions and the characterization of RAI-refractory tumors, the treatment modalities performed (local therapies and/or systemic treatment), the response to therapy and the disease progression rate.

Results: Patients with radioiodine refractory thyroid cancer (RAI-R DTC, n=122, 44.3% men, age-at-diagnosis 51.98±15.8 years, were followed-up for 9.5 years (1.4-50). Patients ≥55 yrs at-diagnosis had more frequently follicular/oncocytic DTC, increased tumor size, metastatic disease and worse outcome (P=0.015) compared to younger. Patients were divided in two groups: those with only cervical persistence (Group 1), n=27 (22.1%), and those with distant metastases (Group 2), n=95(87.9%). In Group1 29.6% underwent >2 surgeries, 14.8% cervical external beam radiation therapy (EBRT), one radiofrequency-ablation (RFA), one sorafenib. The final outcome was: partial response (PR) 4(14.8%), stable disease (SD) 23/27(85.2%). In Group2 40% underwent >2 locoregional surgeries, 28.4% EBRT, 6.3% RFA. For distant metastases 42.1% received local therapies, 47.4% TKIs. Metastases stabilization with local procedures was achieved in 33.7% (18/45 while receiving TKI). Group1 patients were younger, with smaller tumors, had more frequently classical PTC (P=0.005) and more favorable outcome (P<0.001). In Group2 sorafenib was administered in 30 patients (median PFS 1.5 yrs, OS 2.7 yrs), lenvatinib in 31 (median PFS 2 yrs, OS 3.581 yrs), cabozantinib in 7. Overall, for patients with metastatic disease the final outcome was: PR 7/95 (7.4%) SD 38 (40%) PD 50(52.6%), 34/95 (35.8%) died of disease progression, 7/95 (7.4%) died of unrelated causes; in Cox-proportional-hazard analysis, for the total follow-up period, when age-at-diagnosis, TKI administration, local therapies, local surgeries, soft-tissue invasion, tumor size and histology were included in the analysis, the age-at-diagnosis and the administration of local therapies were predictors of more favorable OS and CSS (P<0.02).

Conclusions: In RAI-R thyroid cancer patients with metastatic disease younger age at diagnosis and the implementation of local therapies are associated with a more favorable outcome