SAT526 Limited Utility of Routine Neck Ultrasound Follow-up in Advanced Stage Differentiated Thyroid Cancer

Disclosure: V. Munro: None. S. Mustafa: None. F.S. Siddiqi: None. M. Rajaraman: None. S.A. Imran: None. Background: Most guidelines recommend periodic cervical ultrasound (US) for ongoing surveillance of differentiated thyroid cancer (DTC). While recent studies do not support routine US surveillance in low-risk DTC, to date, no study has assessed the clinical utility of cervical US in advanced DTC. Methods: We conducted a retrospective study of our hospital DTC registry using the following criteria: a) AJCC stage III and IV, b) minimum follow-up of >4 years since total thyroidectomy +/-I-131 ablation, and c) at least one US per 3 years of follow-up. Patients with hemithyroidectomy only or positive anti-thyroglobulin antibody at the initial visit were excluded. Two years after initial treatment, patients were categorized by Dynamic Risk Stratification (DRS) as excellent, indeterminate, biochemically incomplete, or structurally incomplete response. Data obtained at each visit included: treatment response, thyroglobulin (TG) level, and US findings. Results: A total of 114 patients (85 AJCC stage III and 29 stage IV patients) met the inclusion criteria. Mean age (yrs) at diagnosis was 59, and 67% were female. Mean duration of follow-up was 8.5 years. Based on DRS, 73 patients had excellent response, 28 indeterminate, 8 biochemically incomplete, and 5 structurally incomplete. Recurrence or progression was detected in 20 patients (17.5%): 5 excellent response, 6 indeterminate, 5 biochemically incomplete, and 4 structurally incomplete. Recurrence sites included cervical region (14), distant metastases (5) and both (1). The TG rose from a mean of 4.76 ng/mL at baseline to 40.37 ng/mL at time of recurrence/progression. In those with structurally incomplete disease, US demonstrated progression in all 4 patients. However in other DRS categories, only 5/10 had definite US abnormalities. Of those without recurrence, 4 patients (4.3%) had false positive TG (mean baseline TG 0.08 rose to 11.8 ng/ml) without clinical/radiologic recurrence whereas the rate of false positive US abnormalities was 32% (37/114). The sensitivity and specificity of US vs. TG in diagnosing recurrence was 45% and 60% vs 100% and 95.7%, respectively. Conclusion: Our study suggests that routine cervical US surveillance after initial DRS does not improve the detection of recurrence in patients with excellent, indeterminate, or biochemically incomplete disease, and has a high false positive rate. Therefore, we suggest TG should be considered the mainstay of surveillance and any further imaging guided by DRS status and change in TG. Presentation Date: Saturday, June 17, 2023