Prognostic Value of Thyroglobulin Serum Levels and 131I Whole-Body Scan after Initial Treatment of Low-Risk Differentiated Thyroid Cancer

Edelmiro Menéndez Torre; María Teresa López Carballo; Rosa María Rodríguez Erdozáin; Lluís Forga Llenas; María José Goñi Iriarte; Juan José Barbería Layana

Disclosures

Thyroid. 2004;14(4) 

In This Article

Discussion

Following the protocol established in 1987, which is similar to other groups, we studied the evolution of 194 patients diagnosed consecutively with differentiated thyroid carcinoma and treated with total or near-total thyroidectomy followed by high-dose 131I thyroid ablation, in the absence of either anti-Tg autoantibodies and or evidence of distant metastasis. These patients underwent diagnostic 131I-WBS and Tg levels off levothyroxine were determined between 6 and 9 months after treatment. The majority of the patients (86.1%) showed no uptake at the neck, indicating adequate surgical removal. However, uptake was observed in 27 patients and in all cases was limited to the neck.

Both Calloux et al.[11] and Pacini et al.[12] have suggested that when Tg levels are undetectable, this undetectable level has great predictive value of disease-free status and in these cases, whole-body scans provide no additional information.

In our series, these data are confirmed. In a small percentage of patients (4.5%), uptake is observed at the thyroid bed while Tg levels remain undetectable, indicating incomplete surgery. In these patients a new ablative dose of 131I was effective in eradicating disease in all cases and none developed metastases after a mean follow-up of more than 8 years.

Of the 124 patients with undetectable Tg levels and negative WBS, only 2 showed persistence of disease and none developed metastasis after a follow-up period of 8 years. Six patients presented with new uptake on WBS, which was always confined to the thyroid bed and coincidental with an elevation of Tg levels in 5. A new 131I ablative dose was effective, achieving remission in all 5 cases. Another 6 patients showed detectable Tg levels during follow-up period; in all cases levels were below 10 ng/mL, but in 2 cases levels continued to be above 2 ng/mL and none developed metastasis. Thus, undetectable Tg levels off levothyroxine 6 to 9 months after 131I ablation proves to be an excellent predictor of a disease-free state in the long term in the majority of the cases. In those exceptions where relapse occurs, this is confined locally and is detectable by the increments in Tg levels.

On the other hand, when Tg levels are detected with high TSH,[13] the probability of disease is very high. After a mean follow-up period of 8 years, persistence of disease was observed in 47.5 % of those patients, and in more than half of these patients distant metastases were detected. Those patients with initial Tg levels over 10 ng/mL had a worse prognosis,[14,15] given that currently there is still evidence of disease in all of them. Forty percent of those with detectable Tg and negative WBS showed persistence of disease, with evidence of uptake after high doses of radioiodine or in the FDG-PET in a substantial proportion of them, indicating that WBS scarcely provides additional information on the final outcome.

Follow-up of patients with undetectable Tg and negative scans should be carried out by periodic determinations of serum Tg levels with high TSH. Currently Tg determination can be carried out after administration of recombinant human TSH, obviating the need to withdraw levothyroxine with similar results.[16,17]

There is still uncertainty regarding the patients who were Tg undetectable and scan-positive, because we treated 8 of them with a new dose of 131I and might have influenced their final outcome.

To conclude, our results confirm the reliability of Tg levels in serum after withdrawal of levothyroxine in predicting remission of differentiated thyroid carcinoma after thyroidectomy and 131I ablation, and the limited usefulness of diagnostic 131I-WBS. Further diagnostic measures to detect neoplastic foci would only be necessary in those cases in which increments in Tg levels were detected, either by administration of 131I ablative dose,[18] or PET,[19] or CT scan or other radiologic techniques.

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