Thyroglobulin Changes are Highly Dependent on TSH in Low-risk DTC Patients not Treated with Radioiodine

Low-risk differentiated thyroid cancer (DTC) is currently rarely treated with radioiodine (131I) to ablate the postoperative remnant. Therefore, the interpretation of the serum thyroglobulin (Tg) values should be reconsidered. The aim of our study was to evaluate the changes in Tg values during follow-up with regard to the changing values in thyroid stimulating hormone (TSH).

We evaluated 271 low-risk DTC patients, treated with total thyroidectomy but not 131I. To be included, patients had to be negative for Tg antibodies and have at least 3 evaluations in our department. All patients were on levothyroxine (L-T4) therapy.

After a median follow-up of 73 months, the overall Tg values were stable, while TSH values slightly increased. Therefore, we pooled data of Tg and TSH from all evaluations and a significant positive correlation was demonstrated (R = 0.2; P < 0.01), and was also demonstrated when we performed the analysis using time-weighted values (R = 0.14; P = 0.02). Moreover, when dividing patients into 3 groups according to first postoperative Tg (Group A [Tg < 0.2 ng/ml], Group B [Tg 0.2-1 ng/ml], and Group C [Tg > 1 ng/ml]) most patients showed stable values of Tg at the end of follow-up but TSH variations had a clear impact on the changes in Tg among the groups.

We demonstrated that in low-risk DTC not treated with 131I, serum Tg remains substantially stable over time, and the variations observed were correlated with the concomitant variations of TSH levels, mainly due to the modification of LT-4 therapy performed according to the ongoing risk stratification.