Early Sequential Changes in Serum Thyroglobulin After Radioiodine Ablation for Thyroid Cancer: Possible Clinical Implications for Recombinant Human Thyrotropin-Aided Therapy

Abstract

TNM status and posttherapy whole-body scan findings aid in risk stratification of patients with thyroid cancer during initial therapy. Recently, the thyroglobulin (Tg) value measured during hypothyroidism just before 131I therapy (preablation Tg) has proved to be effective for predicting persistent/recurrent disease. In this study, we assessed the changes in serum Tg 48 hours after radioiodine ablative therapy performed in the hypothyroid state in order to evaluate if this parameter could be used in recombinant human thyrotropin (rhTSH)-treated patients. Because rhTSH-stimulated TG is traditionally measured 72 hours after the second injection of rhTSH corresponding to 48 hours post-131I therapy, the time course of serum Tg after radioiodine administration is an important clinical issue. To address this issue, we performed a prospective evaluation of 26 consecutive patients with low-risk differentiated thyroid cancer hypothyroidism for radioiodine ablation (3.7 GBq of 131I). Baseline Tg values were compared to posttherapy Tg values (at 24 and 48 hours). We found that Tg increased after 131I therapy because of the acute radiation effects on residual thyroid cells. Median values at each of the three time points were 1.8 ng/mL (baseline), 3 ng/mL (Tg-24), and 11.3 ng/mL (Tg-48) (Brahms Tg Kryptor assay, Brahms AG, Berlin, Germany). Tg-48 values were not statistically correlated with initial Tg values. Tg-48 remained below 15 ng/mL in 14 of 26 patients. In conclusion, the increase in Tg during the early post-131I therapy period means that first rhTSH-stimulated Tg cannot be used as a corresponding value for preablative hypo-Tg. We discussed whether rhTSH-stimulated Tg value might be useful in a subset of patients. In our opinion, this drawback does not outweight the expected benefits of rhTSH-aided therapy on quality of life of patients and overall cost of the therapy.

Stimulated thyroglobulin level at ablation in differentiated thyroid cancer: the impact of treatment preparation modalities and tumor burden

“…Second, stimulated Tg was measured 2 days after the first rhTSH injection, immediately before the radioiodine treatment, thus resulting in lower Tg values than those expected at 4 days (13,14). The main advantage of assessing rhTSH-stimulated Tg before radioiodine ablation is to overcome the serum Tg increase due to the effects of radiation on thyroid remnants (15). Third, the present data strongly suggest that the stimulated Tg level is related to the burden of PRD.…”

Thyroglobulin measurement before rhTSH‐aided 131I ablation in detecting metastases from differentiated thyroid carcinoma

“…Many reports indicate the usefulness of Tg concentration measurement before radioiodine treatment to early detect DTC relapse or metastases. However, the stimulated Tg cannot be used instead of pre‐ablative offT4‐Tg when rhTSH is employed to prepare radioiodine ablation 3–5,8 . Excluding thyroid cells damage, two factors determine Tg concentration in most clinical situations: thyroid cell mass and activation of TSH receptors 14 .…”

“…The Tg levels must be measured 48 h after radioiodine administration when rhTSH is used as stimulation 7 . Consequently, due to the radioiodine‐induced thyroid cells damage and Tg release, the Tg measurement would not have reliable predictive value in patients stimulated by rhTSH 8 . The present study was then undertaken to evaluate if Tg measurement before rhTSH administration and under T4 (onT4‐Tg) predicts post‐ablative scan results and patients’ outcome.…”

Recombinant human thyroid stimulating hormone in 2008: focus on thyroid cancer management

“…This is after the ablative dose of RAI, which could impact Tg levels on the basis of radiationinduced tumor lysis. One study examined the effect of this intervening ablative dose of RAI on Tg levels and found that Tg levels increased after RAI therapy due to acute radiation effects (Taieb et al 2006). Because of the two simultaneous stimuli to Tg levels, rhTSH and RAI tumor destruction, this paradigm would not result in Tg levels that would be comparable to values obtained in diagnostic settings.…”