Long-term outcomes of distant metastasis from differentiated thyroid carcinoma

Background The aim of this study was to identify the prognostic factors of long-term survival and optimal therapeutic protocol for patients with distant metastasis secondary to differentiated thyroid carcinoma (DTC). Methods A retrospective review of 1665 patients with DTC treated at a regional tertiary hospital in Taiwan between 1986 and 2010 was performed. Among them, 207 patients were found to have distant metastasis. For a long-term outcome survey, 126 patients that had received at least 5 years (mean 9·6 ± 5·2 years) of follow-up after the diagnosis of distant metastasis were analysed for this study. Prognostic factor analysis included age, sex, histology, disease stage, type of surgical procedure, site of metastatic foci, ¹³¹I avidity of tumour, thyroglobulin (Tg) level and accumulated therapeutic dose of radioiodine (RAI). Results The mean age at diagnosis of distant metastasis was 46·4 ± 17·2 years. The female-to-male ratio was 2·1:1. The 10- and 15-year survival rates were 70·6% and 64·9%, respectively. The independent predictors of survival were younger age, surgical dissection of neck lymph nodes (LNs) and low TSH-stimulated Tg level (<400 μg/l) at the discovery of metastasis. Most cases of resolved ¹³¹I-avid disease (79·2%) and disease-free remission (87·5%) received a cumulative dose no >600 mCi of ¹³¹I. The mean cumulative doses of ¹³¹I in both deceased and living patients were similar. Conclusion The prognosis of patients with distant metastasis from DTC within this study was found to be favourable. Survival may be improved by surgical dissection of neck LNs, but repeated ¹³¹I therapy >600 mCi is not advised unless there is a high probability that it would benefit the patient.