Predictive value of recombinant human TSH stimulation and neck ultrasonography in differentiated thyroid cancer patients

Background: Serum thyroglobulin (Tg) stimulation by recombinant human TSH (rhTSH), in combination withneck ultrasonography (US), is an important tool in the first follow-up of differentiated epithelial cell thyroidcarcinoma (DTC) patients. The objective of this study was to investigate if a second rhTSH stimulation, performed2–3 years later, is of clinical utility in the follow-up of these patients.Methods: One hundred and one consecutive ambulatory DTC patients were studied. The great majority of them(89=101) were low-risk patients, being stage I or II at tumor node metastasis (TNM) staging classification. Allstudy patients had been treated by surgery and radioiodine ablation, and exhibited, at first rhTSH follow-up,either undetectable Tg (#1ng=mL) (rhTSH1-Tg, n¼89 patients considered as free of disease) or low Tg (>1–5ng=mL) (rhTSH1-Tg+, n¼12 patients considered with uncertain prognosis), with no US evidence of residualdisease. In all patients, serum Tg measurement after a second rhTSH stimulation and neck US were performed.Results: At the second follow-up, all 89 rhTSH1-Tgpatients showed a negative US, and Tg became low positiveonly in one case, whereas it remained undetectable in the other patients. The overall negative predictive valueof rhTSH1-Tg was, then, 98.9%. Out of the remaining 12 patients (i.e., rhTSH1-Tg+ patients), 2 showed diseasepersistence=recurrence (with a positive predictive value of rhTSH1-Tg+ of 16.7%) and 6 became Tg.Conclusions: A second rhTSH stimulation is useless in DTC patients who were rhTSH-Tg and imaging negativeat first follow-up, while it is suggested in patients with detectable, although low, rhTSH-Tg levels at first followup:in the absence of clinical or US evidence of disease persistence, these patients should not be retreated byradioiodine, but simply scheduled for a later rhTSH stimulation.