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 (131)I 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 >or=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 (131)I uptake in distant metastases and survival was significant (p = 0.0006). The proportion of patients with non-iodine-avid distant metastases that were >or=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.