OR27-5 The De Novo Detection of Anti-Thyroglobulin Antibodies and Differentiated Thyroid Cancer Recurrence

Background: The prevalence and clinical significance of de novo detection of anti-thyroglobulin antibodies (TgAb) during the follow up of patients with differentiated thyroid cancer (DTC), is unknown. Methods: We utilized the National Thyroid Cancer Treatment Cooperative Study registry (1987-2012). Of >5,000 registered DTC subjects, we identified 1,545 subjects who had available TgAb status (TgAb cohort), of whom 1,325 were TgAb negative at first post-operative follow-up testing. From this initial TgAb negative group, we excluded 513 patients: 423 patients who had less than three-years of follow-up and/or fewer than three follow-up visits, 86 patients with persistent disease after initial treatment, and 4 patients with data entry errors. The remaining 812 patients were included for analysis, comprising the TgAb persistently negative group [defined as TgAb negative for at least three consecutive follow-up visits and at least three-years of follow-up] (n = 772) and a de novo TgAb positive group in whom TgAbs became detectable (n = 40). We then assessed whether de novo appearance of TgAb was associated with DTC structural recurrence using the Kaplan-Meier method. Results: The de novo detection of TgAb occurred in 5% of DTC patients. Recurrence of DTC in the TgAb persistently negative group compared with the de novo TgAb positive group did not differ significantly (8.7% vs 13.3%, p = 0.2). Baseline characteristics, histology, history of radiation exposure, staging, and median duration of follow-up were similar between the two groups. Interestingly, in all 6 patients who suffered a recurrence in the de novo TgAb positive group, TgAbs were detected after the recurrence was detected radiologically [median 2.1, 0.7 - 8.7 years]. Conclusion: Utilizing a large North American DTC registry, we found the prevalence of de novo TgAb detection to be 5% among initially TgAb negative patients. We did not find a statistically significant association between de novo TgAb development and DTC structural recurrence. This study is limited by its retrospective design, institutional differences in TgAb assays, and the exclusion of large group of subjects due to lack of TgAb data or inadequate follow up. Furthermore, the small number of actual recurrences limits the power of the analysis to identify an association. Larger prospective studies are required to confirm these findings and further assess the significance of de novo TgAb detection in the follow up of DTC.