The Initial ATA Risk Classification, but Not the AJCC/TNM Stage, Predicts the Persistence or Relapse of Differentiated Thyroid Cancer in Long-Term Surveillance

Background: The American Joint Commission on Cancer on Tumor Node Metastasis (AJCC/TNM) staging system provides adequate information on the risk of differentiated thyroid cancer (DTC)-specific mortality in totally thyroidectomized patients, but its role in predicting persistence and relapse of disease is uncertain. The relatively new 2015 American Thyroid Association (ATA) guidelines recommend stratifying patients at the time of DTC diagnosis with its own risk classification system, in order to identify those at high risk of residual or recurrent morbidity who may benefit from post-operative radioiodine (RAI) administration and/or need additional work-up. Methods: To verify the prevalence proportion of persistence or relapse of disease, a consecutive cohort of 152 patients with a diagnosis of DTC, subjected to total thyroidectomy (+/− post-operative RAI administration as per guidelines indication) and to neck ultrasonography (US), as well as biochemical surveillance for a minimum of 2 years at the Endocrinology Unit of Mater-Domini Hospital (Catanzaro, Italy), was enrolled. The prognostic role of the AJCC/TNM stage and ATA risk classification system was analyzed by logistic regression. Results: At a mean of 9 years after surgical treatment, DTC was found to persist or relapse in 19 (12.5%) participants. The initial risk for these outcomes, based on the ATA classification, was mostly low (53.9%) or intermediate (39.5%). AJCC/TNM stages were predominantly stage I or stage II. Despite a small representation in this cohort, high-risk patients according to the ATA classification had 8-fold higher odds of persistence or relapse of disease than those of low-risk participants, while controlling for potential risk modifiers, including age at DTC diagnosis, male gender, and post-operative RAI administration (p = 0.008). In contrast, the AJCC/TNM stage was not associated with the disease status at the last follow-up visit (p = 0.068 for the 7th Edition; p = 0.165 for the 8th Edition). Furthermore, low-risk participants subjected to post-operative RAI administration had the same probability of persistence or relapse of DTC when compared to those who had undergone total thyroidectomy only. Conclusions: There is a need for the endocrine community to revise the current work-up of DTC. The initial ATA risk classification is a reliable tool for predicting the persistence or relapse of disease in long-term surveillance.