Comparison of the usefulness of post-ablative and post-operative thyroglobulin concentration measuring in prognostic assessment of patients with differentiated thyroid cancer

Introduction: Post-operative thyroglobulin (TgPO) is a recognised prognostic factor in patients following thyroidectomy due to differentiated thyroid cancer (DTC). However, its concentration is affected by thyroid remnants, which may diminish the prognostic value of TgPO. The aim of this paper is to assess the usefulness of stimulated post-ablative thyroglobulin (TgPA) measurements 6-9 months after I-131 therapy, as a prognostic factor, and its possible advantage over TgPO determination. Material and methods: The study involved 577 DTC patients treated in the Holycross Cancer Centre in the years 2000-2013. Exclusion criteria were: patients with no recommendation for 131I adjuvant therapy, positive thyroglobulin antibody titre, and initial distant metastases. On the basis of a ROC curve analysis, values of TgPO and TgPA concentrations were determined, which enable the most accurate identification of good prognosis. Calculating area under the curves (AUCs) allowed for comparison of the data. Results: TgPO concentration <= 6.99 ng/mL, with 75.7% sensitivity and 94.7% specificity enables anticipation of remission of the disease. TgPA concentration <= 1.16 ng/mL under endogenous TSH stimulation with sensitivity of 91.1% and specificity of 94.7% allows anticipation of remission of the disease. TgPA concentration <= 1.24 ng/mL under rh TSH stimulation with sensitivity of 95.4% and specificity of 95.0% enables anticipation of remission of the disease. Conclusions: No differences in clinical usefulness of the assessment of TgPO and stimulated TgPA concentrations as indicators of good prognosis were found. However, TgPA allows anticipation of remission of the disease with higher sensitivity. It also appears that TgPA may be of particular prognostic importance in baseline high-risk patients (pT3-T4/N1). A sufficiently low TgPA concentration, demonstrating good response to I-131 adjuvant therapy in these groups, is an indicator of improved prognosis.