Usefulness of the combined antithyroglobulin antibodies and thyroglobulin assay in the follow-up of patients with differentiated thyroid cancer

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Abstract
A total of 1050 patients with differentiated thyroid cancer (DTC) have been followed in the Thyroid Center of Padua by means of serum thyroglobulin (Tg) measured with IRMA method and anti-Tg antibodies (TgAb) assays. Circulating TgAbs were detected in 102 (9.7%) patients. In 32 of these 102, TgAbs were evaluated before and after total thyroidectomy and 131l ablation. In these patients no relationship was found between preoperative serum TgAb levels on the one hand and tumor stage at diagnosis or outcome of the disease on the other. During the follow-up, TgAb serum levels decreased or disappeared in 21 cases considered tumor-free, while they remained unchanged or even increased, in comparison with the preoperative ones, in 11 patients, 5 with proven metastases and 6 considered tumor-free. Evaluating the whole group of 102 TgAb-positive patients, we observed that TgAb serum levels, measured after thyroid ablation, were significantly higher in cases with metastases than in those considered tumor-free (653.0 ± 196.9 vs 157.7 ± 116.5 U/ml, m ± SD, p < 0.0001). In the group of patients with metastases and circulating TgAbs, Tg serum levels were elevated in 27% of cases on TSH- suppressive therapy and in 44% off therapy when nodal metastases were present, and in 67% of cases on TSH-suppressive therapy and in 83% off therapy when distant metastases were present. Our data suggest that: i) In a very large series of patients with DTC, circulating TgAbs are detectable in 9.7% of cases; ii) In the follow-up, patients with high TgAb serum levels even in absence of detectable serum Tg values are at risk for metastases; in fact circulating TgAbs might be due to the presence of tumor and circulating TgAbs themselves may prevent the detection of serum Tg; iii) serum IRMA-Tg assay appears to maintain its value as a tumoral marker in more than half the patients with metastases and circulating TgAbs.