Treatment-Free Survival in Patients With Differentiated Thyroid Cancer

Objective Cancer recurrence is a primary concern for patients with differentiated thyroid cancer; however, population-level data on recurrent or persistent disease do not currently exist. The objective of this study was to determine treated recurrent or persistent thyroid cancer by using a population-based registry, identify correlates of poor treatment-free survival, and define prognostic groups for treatment-free survival. Methods In this population-based study, we evaluated treatment-free survival in 9273 patients from the Surveillance, Epidemiology, and End Results Program–Medicare with a diagnosis of differentiated thyroid cancer between 1998 and 2012. Treated recurrence was defined by treatment of recurrent or persistent differentiated thyroid cancer with surgery, radioactive iodine, or radiation therapy at ≥1 year after diagnosis. Multivariable analysis was performed with Cox proportional hazards regression, survival trees, and random survival forests. Results In this cohort the median patient age at time of diagnosis was 69 years, and 75% of the patients were female. Using survival tree analyses, we identified five distinct prognostic groups (P < 0.001), with a prediction accuracy of 88.7%. The 5-year treatment-free survival rates of these prognostic groups were 96%, 91%, 85%, 72%, and 52%, respectively, and the 10-year treatment-free survival rates were 94%, 87%, 80%, 64%, and 39%. Based on survival forest analysis, the most important factors for predicting treatment-free survival were stage, tumor size, and receipt of radioactive iodine. Conclusion In this population-based cohort, five prognostic groups for treatment-free survival were identified. Understanding treatment-free survival has implications for the care and long-term surveillance of patients with differentiated thyroid cancer.