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Rising serum antithyroglobulin antibody levels predict recurrence of differentiated thyroid carcinoma in thyroglobulin-negative patients

01/2008;

ABSTRACT SUMMARY BACKGROUND Serum antithyroglobulin antibodies (TgAbs) are found in 10 to 25% of patients with differentiated thyroid carcinoma (DTC), as compared with an incidence of approximately 10% in the general population. This poses a serious problem in the follow-up of patients with DTC, as circulating TgAb interferes with serum thyroglobulin (Tg) measurements performed by immunometric assays. Thyroid cancer management guidelines suggest that TgAb levels serve as a surrogate for serum Tg measurement during follow-up, providing TgAb is measured in the same laboratory. Kim et al. hypothesize that changes in serum TgAb might predict tumor outcome, which has been a point of contention in previous studies. The aim of this study was to determine whether a changing pattern of TgAb levels found soon after thyroidectomy could serve as a prognostic indicator. METHODS This retrospective study was performed on 1499 consecutive patients treated for DTC in the authors' hospital from 1995 through 2003. All had total thyroidectomy followed by remnant ablation with 100 to 150 mCi (3.7 to 5.55 GBq) of 131 I about 6 weeks after surgery. Patients selected for study had no preoperative evidence of extracervical tumor, or 131 I uptake outside the thyroid bed on the posttreatment whole-body scan (RxWBS) or in the thyroid bed on the first diagnostic whole-body scan (DxWBS) during follow-up. Patients with extracervical metastases or poorly differentiated or anaplastic thyroid cancer were excluded from the study. Follow-up DxWBS was performed with 4 mCi (148 MBq) of 131 I after thyroid hormone withdrawal every 3 to 6 months along with serum Tg and TgAb measurements. When serum Tg was above

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    ABSTRACT: Cross-sectional studies have reported an increased prevalence of circulating thyroglobulin autoantibodies (TgAbs) in patients with differentiated thyroid carcinoma (DTC). With the advent of more sensitive assays, a longitudinal study monitoring the development of TgAb levels after ablative therapy was warranted. One hundred and twelve consecutive patients with follicular cell-derived thyroid cancer were followed for 3 years. All patients had been thyroidectomized and received, on average, two radioiodine therapies. Residual tissue was quantified scintigraphically by 131I 24-h uptake. TgAb and thyroglobulin (Tg) serum levels were determined with a sensitive direct radioligand assay and an IRMA respectively. The prevalence of TgAbs at the initial examination was 29% (median 130 U/ml). During follow-up, TgAb levels rose transiently in one-tenth of the patients, but the prevalence of demonstrable TgAbs decreased to < 10% after 3 years. The median serum half-life of TgAbs in treated DTC patients was 10 weeks. At initial examination (when all patients still had residual thyroid tissue and 17 had metastases), rising TgAb levels were correlated with the inability to detect Tg in 4, 30 and 73% of the patients, when initial TgAbs were < 6, 6-50 or > 50 U/ml respectively. While the Tg recovery test was valid for all patients, an in vitro dilution assay with TgAb serum reduced Tg values by up to 32%. The development and course of TgAbs in DTC patients cannot be predicted by initial or residual tumour volume, TgAb or Tg levels. The presence of TgAbs, even in low concentrations, may cause Tg underestimation despite valid recovery tests in DTC patients.
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