Circulating human thyroglobulin (TG) measurement has a pivotal role in the management of patients affected by differentiated thyroid cancer (DTC). Undetectable thyrotropin (TSH)-stimulated serum TG after thyroid ablation (i.e., thyroidectomy and radioiodine) implies the absence of residual or relapsing DTC. Recently, high-cost recombinant human TSH (rhTSH) was proposed for TG stimulation to avoid uncomfortable thyroxine (T4) withdrawal. However, only a small fraction of relapsing DTC patients showed undetectable TG under T4 treatment (onT4-TG) by high-sensitivity assays. The present study was undertaken to compare onT4-TG with the rhTSH-stimulated TG assay (rhTSH-TG), 131I scanning and neck ultrasound (US) with fine-needle aspiration biopsy.Methods
We enrolled 117 patients with histologically proven DTC treated by total thyroidectomy and radioiodine. Inclusion criteria were: complete tumour excision, no radioiodine uptake outside of the thyroid bed at post-treatment scan and undetectable on T4-TG 3 months after primary treatment. At 1 year after radioiodine treatment, all patients underwent onT4-TG assay, rhTSH-stimulated TG assay, 131I scanning and neck US. Based on histology, clinical data and long-term follow-up, persistent/relapsing disease was confirmed in 14 patients.Results
onT4- and rhTSH-TG were positive in 10 and 12 patients, respectively and two patients converted from undetectable to detectable TG after rhTSH administration. Neck US was positive in 10 patients and a combination of US with onT4- and rhTSH-TG assays showed positivity in 13 and 14 out 14 patients, respectively. A radioiodine scan was positive in six patients, all with positive onT4- and rhTSH-TG levels. Globally, the negative predictive value of the onT4-and rhTSH-TG assays was 99% and 100%, respectively, and 104 rhTSH stimulations had to be performed to detect one local recurrence with negative onT4-TG. Conclusions: Our preliminary data need further confirmation on larger groups of patients, but seem to indicate that onT4-TG assay by a high-sensitivity method combined with neck US may avoid rhTSH stimulation in low-risk DTC patients after surgery and radioiodine thyroid ablation.