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

Summary 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.