Does an undetectable rhTSH‐stimulated Tg level 12 months after initial treatment of thyroid cancer indicate remission?

Abstract

Routine monitoring after the initial treatment of differentiated thyroid cancer (DTC) includes periodic cervical ultrasonography (US) and measurement of serum thyroglobulin (Tg) during thyrotrophin (TSH) suppression and after recombinant human TSH (rhTSH) stimulation. The aim of our study was to evaluate the utility of repeated rhTSH-stimulated Tg measurements in patients with DTC who have had no evidence of disease at their initial rhTSH stimulation test performed 1 year after the treatment. A retrospective chart review of 278 patients with DTC who had repeated rhTSH stimulation testing after an initial undetectable rhTSH-stimulated serum Tg level. The number of rhTSH stimulation tests performed on individual patients during the follow-up period (3-12 years, mean 6·3) varied from two to seven. Biochemical and/or cytological evidence of potential persistent/recurrent disease based on detectable second or third rhTSH-stimulated Tg values and US findings was observed in 11 (4%) patients. Subsequent follow-up data revealed that in five cases, the results of the second stimulation were false positive, in one case - false negative. Combined with the negative neck US, the negative predictive value for disease-free survival was 98% after the first undetectable rhTSH-stimulated Tg and 100% after the second one. In patients with DTC, the intensity of follow-up should be adjusted to new risk estimates evolving with time. The first rhTSH-stimulated Tg is an excellent predictor for remission, independent of clinical stage at presentation. Second negative rhTSH-Tg stimulation is additionally reassuring and can guide less aggressive follow-up by the measurement of nonstimulated Tg and neck US every few years.