Evaluating the 2015 American Thyroid Association Risk Stratification System in High-Risk Papillary and Follicular Thyroid Cancer Patients

Background: The 2015 American Thyroid Association (ATA) Risk Stratification System for differentiated thyroid cancer (DTC) is designed to predict recurring/persisting disease but not survival. Earlier studies evaluating this system evaluated the 2009 edition, comprised a low number of patients with ATA high-risk, had low numbers of patients with follicular thyroid cancer (FTC), or did not distinguish between papillary and FTC. Therefore, we evaluated the prognostic value of the 2015 ATA Risk Stratification System in a large population of high-risk thyroid cancer patients, which included a substantial proportion of FTC patients. Methods: We retrospectively studied adult patients with DTC who were diagnosed and/or treated at a Dutch university hospital between January 2002 and December 2015. All patients fulfilled the 2015 ATA high-risk criteria. Overall survival and disease-specific survival (DSS) were analyzed using the Kaplan-Meier method. Logistic regression and Cox proportional hazards models were used to estimate the effects of DTC subtype and ATA high-risk criteria on response to therapy, recurrence, as well as survival. Results: We included 236 patients with high-risk DTC (32% FTC) with a mean age of 56 years. Median follow-up was 6 years. At final follow-up, 69 patients (29%) had excellent response, while 120 (51%) had structural disease. All high-risk criteria, except large pathologic lymph nodes, were inversely related to excellent response and positively related to structural disease at final follow-up. During follow-up, 14% of the 79 patients who achieved excellent response developed a recurrence. Finally, 10-year DSS was much higher in the initial excellent response than in the initial structural disease group (100% vs. 61%, respectively). Conclusions: In a population of high-risk DTC patients harboring a large subset of FTC patients, the 2015 ATA Risk Stratification System is not only an excellent predictor of persisting disease but also of survival. As much as 14% of the high-risk patients who had an excellent response upon dynamic risk stratification experienced a recurrence during follow-up. Clinicians should thus be aware of the relatively high recurrence risk in these patients, even after an excellent response to therapy.