Long-Term Prognostic Value of the Response to Therapy Assessed by Laboratory and Imaging Findings in Patients with Differentiated Thyroid Cancer

This study assessed the long-term predictive value of the response to therapy, evaluated by serum thyroglobulin (Tg) determination and neck ultrasound, and estimated the potential additional impact of diagnostic whole-body scan (WBS) in patients with differentiated thyroid cancer (DTC) treated with surgery and radioactive iodine (RAI) therapy. We retrospectively evaluated 606 DTC patients treated with surgery and RAI. Response to 131I therapy at 12 months was assessed by serum Tg measurement, neck ultrasound, and diagnostic WBS. According to American Thyroid Association (ATA) guidelines, patients were classified as having a low, intermediate or high risk of recurrence and at 12 months as having an excellent response (ER) or no-ER. Follow-up was then performed every 6–12 months with serum Tg determination and imaging procedures. With a median follow-up of 105 months (range 10–384), 42 (7%) events requiring further treatments occurred. Twenty-five patients had additional RAI therapy, 11 with structural disease in the thyroid bed, eight in both thyroid bed and neck lymph nodes, four had lung metastases and two had bone metastases. The other 17 patients had additional surgery for nodal disease followed by RAI therapy. The ATA intermediate and high risk of recurrence, post-operative and pre-RAI therapy Tg 10 ng/mL, and the absence of ER at 12 months were independent predictors of events. Diagnostic WBS at 12 months permitted the identification of only five recurrences among the 219 ER patients according to serum Tg levels and ultrasound. In DTC patients, the response to therapy at 12 months after RAI therapy could rely on serum Tg measurement and neck ultrasound, while diagnostic WBS was not routinely indicated in patients considered in ER.