Endocrine Abstracts

Thyroglobulin (Tg) is a highly sensitive tumor marker of differentiated thyroid cancer (DTC). To optimize the sensitivity, guidelines recommend Tg measurement after stimulation with recombinant TSH (rh-TSH) 6–12 months after radio remnant ablation (RRA). Based on recent evidence in Literature, it is possible to avoid the measurement of Tg after stimulation with rh-TSH (S-Tg) in presence of undetectable values of basal Tg (B-Tg) if high functional sensitivity (0.1 ng/ml) method is used. However, most patients enrolled in the available studies are affected by low-risk DTC, while there are less evidence in intermediate and high risk patients.

A retrospective analysis on 113 intermediate or high risk DTC patients has been performed. Risk stratification has been evaluated on the basis of 2009 ATA guidelines but our data were also considered on the basis of new ATA guidelines (2015).

Patients were tested for B-Tg and S-Tg. All patients with undetectable B-Tg showed S-Tg <1 ng/ml (sensitivity: 100%). B-Tg cut-off showing best sensitivity and specificity (100% and 99% respectively) in predicting S-Tg <2 ng/ml was 0.22 ng/ml while in predicting S-Tg <1 ng/ml was 0.09 ng/ml (sensibility 100%, specificity 86%).

The cut-off appeared independent from the variables analyzed (pT, N, M, aggressive variants). Moreover, the cut-off appeared independent from Tg values during thyroid hormone withdrawal at the moment of radio remnant ablation.

We conclude that undetectable B-Tg values can predict the biochemical remission of DTC alternatively to S-Tg if high sensitivity assay is used, also in patients with intermediate or high risk DTC.