Evaluation of Factors Associated with Recurrent Differentiated Thyroid Cancer in Patients Who Underwent Total Thyroidectomy and Radioiodine Therapy with Biochemical Incomplete Responses

Objective: The objectives of the present study were 1) to evaluate the factors that predict the recurrence of thyroid cancer in patients with biochemical incomplete responses (BIR) and differentiated thyroid cancer (DTC) patients who were treated with total thyroidectomy and radioiodine-131, 2) to determine the distribution and location of recurrences, and 3) to assess the serial serum thyroglobulin (Tg) and thyroglobulin antibodies (TgAb) to determine the diagnostic accuracy for disease recurrence. Materials and Methods: The authors retrospectively reviewed 203 BIR patients treated between January 2004 and December 2014. Data were recorded on case report forms, including age at the time of first radioiodine-131 treatment, gender, diagnosis, surgical history, Tg and TgAb levels, pathological examination results, and radiology findings from radioiodine-131 whole-body scanning, computed tomography (CT), neck ultrasound, and F-18 FDG PET/CT scans. The 203 patients were classified into two groups, recurrence patients with 54 patients (26.6%), and non-recurrence patients with 149 patients (73.4%). Results: The number and percentage of local recurrences or metastatic lesions were cervical lymph node metastasis in 26 patients (48.1%), local recurrence in 18 patients (33.3%), lung metastasis in 11 patients (20.4%), and bone metastasis in one patient (1.9%). Two patients had lesions in both the surgical site and cervical lymph nodes. Statistically significant clinical characteristics between the two groups included age, the American Thyroid Association (ATA) 2015 risk of recurrence, and lymph node metastasis. Optimal thresholds for recurrence were identified as a Tg velocity greater than 0.6 ng/mL/year, a Tg doubling time of less than 3.5 years, and a TgAb velocity greater than 0 IU/mL/year. Conclusion: Risk factors for local recurrences or metastatic lesions in BIR patients include older age, lymph node metastasis, ATA high risk stratification, Tg velocity at 0.6 ng/mL/year or greater, Tg doubling time in less than 3.5 years, and TgAb velocity greater than 0 IU/mL/year. Close follow-up with CT neck and chest is recommended to detect cervical lymph node metastasis, local recurrences, and lung metastasis.