The goal was todetermine the optimal methods of postoperative monitoring of serum thyroglobulin (Tg) in differentiated thyroid cancer (DTC). This research intended to compare the prognostic value of immunometric methods with different functional sensitivity (FS) for Tg measurement for detecting recurrent disease.
Design: During 2010–2012 years, 76 patients with treated DTC (a total thyroidectomy and adjuvant radioiodine therapy) were included. All patients were at low-to-intermediate risk group(disease advanced was T1–3N0–1M0), the prevalence of TgAb was 36% (n = 27).
The study protocol contained the obtaining of samples biochemical markers twice in year: basal Tg on levothyroxine (L-T4) treatment (bTg), Tg after TSH stimulation test (stTg), TSH, TgAb.
In all cases bTg samplings were investigated with immunometric method with functional sensitivity (FS) –0.9 ng/ml and by high-sensitive assays (hs-bTg) with FS ≤ 0.2 ng/ml.
In 80% of patients, TSH stimulation tests were performed by withdrawal of LT4, in other cases through injection of rhTSH.
The observation period is not less than 6 years.
Results: During first 18 months of follow-up, 9 (12%) patients completed the study suffered from treatment failure (it was confirmed by TSH stimulation test – stTg in the range of 4.5–9.7 ng/ml). In these 9 patients the values of hs-bTg were between 0.54–0.89 ng/ml. The observation continued on 67 patients.
The high sensitivity assays confidently predict increases in stTg after withdrawal LT4 in the absence of TgAb. It appears that in TgAb-negative patients with undetectable bTg a negative TSH stimulation test (stTg ≤ 2.0 ng/ml) can be predicted if their hs-bTg ≤ 0.4 ng/ml. TSH stimulation test detected disease recurrence in two TgAb-positive patients with undetectable bTg and hs-bTg was 0.54 and 0.71 ng/ml resp. High-sensitivity Tg tests demonstrated low reproducibility for all TgAb-positive patients, while in TgAb-negative patients all results were reliable. There was no correlation between the level of TgAb and level of basal Tg and treatment failure.
Conclusions: The Tg obtained after TSH-stimulation is still excellent tumor marker.
When TgAb is absent, bTg measurement by high-sensitivity test and neck US are sufficient tools for routine follow-up of patients with DTC – to monitor the bTg trend without performing any TSH stimulation in patients with initial confirmed low-to-intermediate recurrence risk The influence of TgAb significantly reduces the diagnostic value of Tg assessment. When TgAb is present, the monitoring of bTg by high-sensitivity test can’t replace completely TSH stimulating test.
Funding: This research is performed under Russian scientific fond grant (RSF) №17–75–30 035.
05 Sep 2020 - 09 Sep 2020