Prognostic factors and the effect of treatment with radioactive iodine and external beam radiation on patients with differentiated thyroid cancer seen at a single institution over 40 years

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Abstract
Objectives To assess the prognostic factors and the role of radioactive iodine (RAI) and external beam radiotherapy (RT) in patients with differentiated thyroid cancer. Design A retrospective review of 729 patients treated between 1958 and 1998. The median follow-up was 11·3 years (range 0·3–39·8 years). Primary outcomes included time to cause-specific survival and time to local–regional relapse. Baseline and treatment variables were assessed for statistical significance using the Cox proportional hazards model. Results The 10-year cause-specific survival (CSS) was 87·3% and the 10-year local–regional relapse-free rate (LRFR) was 84·9%. In multivariate analysis there was no statistically significant improvement in CSS with more aggressive treatment (i.e. more extensive surgery, the administration of RAI and/or RT). By multivariate analysis the use of RAI resulted in a statistically significant improvement in LRFR (hazard ratio 0·5; 95% confidence interval 0·3–0·8; P = 0·007). In low-risk patients at AJCC stage I ≤ 45 years, there was no apparent benefit from RAI. For patients over 60, with extrathyroid extension but no gross residual disease (n = 70), adjuvant external RT resulted in statistically significantly higher CSS (10-year CSS 81·0%vs. 64·6%, P = 0·04) and LRFR (10-year LRFR 86·4%vs. 65·7%, P = 0·01). Conclusions The use of RAI was associated with improved LRFR but not in low-risk patients. External beam RT improved LRFR and CSS in high-risk patients.