Thyroglobulin assay 4 weeks after thyroidectomy predicts outcome in low-risk papillary thyroid carcinoma.

BACKGROUND

Thyroidectomy followed by administration of large activities of 131I is the treatment of choice for differentiated thyroid carcinomas. Due to its good prognosis, some authors argue that papillary thyroid cancer with a diameter of up to 10 mm can be treated by surgery alone. In the new TNM classification started in 2002, the T1 group now encompasses all tumours with a diameter up to 20 mm, which widens the indications for a conservative approach. In this instance, prognostic markers are needed to better select patients before planning non-aggressive treatment. Serum thyroglobulin plays a pivotal role in thyroid carcinoma management after thyroid ablation (i.e., surgery and radioiodine) but is of limited value before these treatments. However, thyroglobulin assay performed after surgery but before radioiodine treatment has been proven to be useful in predicting the presence/absence of distant metastasis.

PATIENTS AND METHODS

Our study was undertaken in patients affected by pT1 papillary thyroid carcinoma to evaluate the predictive value of post-surgery thyroglobulin assay on 1) restaging immediately after radioiodine treatment and 2) restaging at 12 months. We selected 156 patients affected by pT1 histologically proven papillary thyroid carcinoma, submitted to total thyroidectomy. Serum thyroglobulin was assayed by a specific immunoradiometric method 4 weeks after surgery, just before radioiodine administration. Cut-off levels were selected by receiver operating characteristic curve analysis. Thyroglobulin levels were compared to the results of a post-radioiodine treatment scan and 12-month restaging.

RESULTS

Globally, 23 out of 156 patients showed persistent/recurrent disease (15%). Post-surgery thyroglobulin levels above 4.50 microg/L identified 94% of patients with metastasis at post-dose scan, and a level below 3.20 microg/L identified 86% and 93% of relapsed and disease-free patients at 12-month restaging, respectively. Multivariate analysis and Spearman rank correlation showed that the N-status and post-surgery thyroglobulin level are independent prognostic factors.

CONCLUSIONS

The post-surgery thyroglobulin level could be systematically assayed in patients with pT1-papillary thyroid carcinoma and taken into account in planning treatment.