The Importance of Age over Radioiodine Avidity as a Prognostic Factor in Differentiated Thyroid Carcinoma with Distant Metastases

Background: Differentiated thyroid carcinoma (DTC) usually has a good prognosis and rarely develops distant metastases. Although it might be expected that avid radioiodine uptake in distant metastases would be associated with a favorable outcome, there are few long-term studies regarding this. The present study was performed to evaluate the influence of radioiodine uptake in distant metastases on the disease-specific survival (DSS) in DTC patients. Methods: This retrospective study included 77 DTC patients with distant metastases (M1) who were treated with I-131 therapy from 1977 to the end of 2000 in our institution. The median follow-up of patients was 6.1 years. Univariate and multivariate analysis were performed using the Kaplan-Meier method and log rank test, and Cox Regression model, respectively. Results: Seventy-seven patients with M1 included 51 (66.2%) women and 26 (33.8%) men; 32 (41.6%) patients were <45 years old and 45 (58.4%) patients were >= 45 years old (range: 8-70 years; mean age: 45.4 years); histologically, there were 54 (70.1%) papillary carcinomas, 22 (28.6%) follicular carcinomas, and one case (1.3%) with an inconclusive histological report. The probability of DSS after appearance of M1 was 57.95% after 5 years, 48.31% after 10 years, and 39.46% after 15 and 20 years. In patients with iodine-avid distant metastases the 5-year DSS was 66.54%, the 10-year DSS was 55.09%, and the 15- and 20-year DSS were 44.99%. In contrast, patients with non-iodine-avid lesions had a 5- and 10-year DSS of 18.33%. This difference relating to the relationship between I-131 uptake in distant metastases and survival was significant (p = 0.0006). The proportion of patients with non-iodine-avid distant metastases that were >= 45 years old was significantly greater than the proportion of patients with non-iodine-avid distant metastases that were <45 years old (p < 0.01). If patients were matched for age, iodine non-avidity significantly shortened the survival in patients < 45 years old (p < 0.001). According to multivariate analysis age had significantly greater influence on survival compared with iodine avidity (p < 0.001, p = 0.078, respectively). Conclusion: Patients with distant metastases have a long-term survival that depends, in addition to other factors, on age and the degree of radioiodine uptake in distant metastases.