Prognostic value of thyroglobulin after thyroidectomy before ablative radioiodine therapy in thyroid cancer

Serum thyroglobulin (Tg) is a suitable marker for differentiated thyroid carcinoma after total thyroid ablation by surgery and 131I therapy. Before the first 131I treatment, Tg is not a reliable tumor marker since it can also originate from remnant tissue. It was hypothesized that the ratio of serum Tg to 131I uptake in the thyroid bed could be used to correct Tg values for variations in remnant tissue.

The hypothesis was evaluated in 111 patients with differentiated thyroid cancer (38 follicular/73 papillary). Tg and 131I uptake in the thyroid bed were measured before the first 131I therapy. The ratio of Tg to 131I uptake was determined in four groups: Group A, tumor free (n = 81); Group B, lymph node metastases (n = 11); Group C, distant metastases (n = 11); Group D, later recurrence [during a mean follow-up of 56 mo; (n = 8)]. Wilcoxon two-sample test was performed to determine statistical significance between Group A and Groups B-D.

Significant differences in the Tg/131I uptake ratios (median) between Group A (1.0 ng/ml/%) and Groups B (3.3 ng/ml/%) and D (3.3 ng/ml/%) were observed (p < 0.01). In tumor-free patients (Group A), there was no value higher than 5.7 ng/ml/%. Therefore, a higher ratio, observed in 14 of the 30 remaining patients, was indicative of metastases or later recurrence.

The ratio of serum Tg to 131I uptake in the thyroid bed might be used as a prognostic marker for thyroid cancer before implementing ablation with 131I.