Changes in Serum Thyroglobulin Levels After Lobectomy in Patients with Low-Risk Papillary Thyroid Cancer

Background: Low-risk patients with differentiated thyroid cancer can be treated with thyroid lobectomy. Serial measurements of serum thyroglobulin (Tg) are recommended for surveillance, but the cutoff values indicating recurrence are not known. This study documented the natural course of serum Tg levels during follow-up after lobectomy for low-risk papillary thyroid carcinoma (PTC) and evaluated whether changes in serum Tg levels predict disease recurrence. Methods: This historical cohort study included 208 patients with low-risk PTC who underwent lobectomy but did not require hormone replacement. Postoperative serum Tg levels and Tg/thyrotropin (TSH) ratios and neck ultrasound were evaluated during a follow-up period with a median of 6.9 years. Results: The serum Tg levels increased gradually, and the proportion of patients with levels >10ng/dL increased annually by 13.9%, 18.8%, 22.1%, 21.9%, 28.4%, and 28.9% during the six-year follow-up period (beta=0.574, p=0.027). The relative serum Tg levels increased by 10% annually (beta=0.105, p<0.001), and the levels of Tg and Tg/TSH ratios in 19 patients with recurrent disease did not differ significantly (beta=0.150, p=0.090). Patients without recurrent disease were more likely to have serum Tg levels increased by >20% (p=0.022). There were no significant differences in the proportions of patients with serum Tg levels increased by >= 50% or 100% in terms of the disease recurrence. Conclusions: Serum Tg levels and the Tg/TSH ratio increased gradually after lobectomy in patients with and without recurrences, without any significant differences. Periodic measurements of serum Tg levels seem to have limited value in predicting recurrent PTCs after lobectomy.