Low levels of serum thyroglobulin after withdrawal of thyroid suppression therapy in the follow up of differentiated thyroid carcinoma

Abstract

We evaluated the reliability of very low serum thyroglobulin (Tg) levels (less than 3 ng/ml) obtained after withdrawal of thyroid suppression therapy in 224 patients without anti-Tg antibodies, who had undergone total thyroidectomy (125 patients) or thyroidectomy followed by 1 or more courses of 131I therapy (99 patients), by performing whole body scans after a therapeutic course of 131I given at the same time of Tg measurement. In 79 patients (35%) a positive scan, associated with a very low level of Tg, was noted. The 131I uptake was limited to the thyroid bed in 60 patients, but metastases were demonstrated in 19 patients (8.5%). These results are mainly explained by the much improved performance of scintigraphy after administration of therapeutic doses of 131I. In the majority of patients, especially those whose 131I uptake was limited to the thyroid bed, further scans were negative. Therefore, in these cases, negative Tg values can generally be considered an early indication of satisfactory evolution. However, in 8.5% of all cases, very low Tg levels were associated with metastases. Thus the follow up of thyroid cancer should not rely only upon Tg determination, even after suppression therapy withdrawal.

Undetectable pre-ablation thyroglobulin levels in patients with differentiated thyroid cancer: it is not always what it seems

“…Although undetectable pre-ablation Tg levels usually indicate complete previous surgery, our data reinforce earlier observations that, in a low percentage of patients, this situation may be related to non-detectable Tg or to the presence of TgAb (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)31). We believe that, when concurrent chronic thyroiditis is found by the pathologist, or when initial TNM stages are diswith DTC, compared with the 10% generally seen in the general population (20).…”

“…Despite the introduction of a Tg reference preparation (CRM 457) more than 10 years ago (18), current methods to measure Tg still have an unacceptable intermethod variability (14,19), and this issue would need to be addressed before considering Tg as a marker of the presence of thyroid tissue. On top of that, false negative Tg levels from 4 up to 35% of DTC patients with evidence of local or metastatic disease have been reported in literature (20)(21)(22)(23)(24).…”

The follow-up of patients with differentiated thyroid cancer and undetectable thyroglobulin (Tg) and Tg antibodies during ablation

“…False negative Tg from 4 up to 35% in DTC patients with evidence of local or metastatic disease had been reported in literature (5)(6)(7)(8)(9). Besides, undetectable serum Tg in patients who have already been treated with 131 I should also not be considered as a reliable criterium to exclude small volumes of persistent or recurrent disease (10)(11)(12)(13)(14).…”

The role of stimulated tireoglobulin in the management of patients with differentiated thyroid carcinoma

“…U studiji Parka i saradnika su naglašena ograniĉenja i nedostaci metodologije praćenja pacijenata sa DTK koja je bazirana samo na sTg, posebno jer su nalazi sTg nedijagnostiĉki u sluĉaju prisustva TgAb [15][16][17]. Niske vrednosti Tg kod pacijenata sa rezidualnim tireoidnim kancerom mogu biti posledica male tumorske mase, prisustva agresivnijih tumorskih formi i slabe diferencijacije tumora sa niskim kapacitetom sekrecije Tg, ili je sekretovani Tg u formi koja ne moţe biti prepoznata rutinskim imunoesejima [18,19]. Najzad, treba istaći da kod jednog broja obolelih od DTK nakon odreĊenog perioda leĉenja dolazi do dediferencijacije tumorskih ćelija i gubitka sposobnosti akumuliranja radiojoda.…”