PROGNOSTIC VALUE OF THYROGLOBULIN AFTER THYROIDECTOMY BEFORE ABLATIVERADIOIODINE THERAPY IN THYROID-CANCER

Serum thyroglobulin (Tg) is a suitable marker for differentiated thyro id carcinoma after total thyroid ablation by surgery and I-131 therapy . Before the first I-131 treatment, Tg is not a reliable tumor marker since it can also originate from remnant tissue. It was hypothesized t hat the ratio of serum Tg to I-131 uptake in the thyroid bed could be used to correct Tg values for variations in remnant tissue. Methods: T he hypothesis was evaluated in 111 patients with differentiated thyroi d cancer (38 follicular/73 papillary). Tg and I-131 uptake in the thyr oid bed were measured before the first I-131 therapy. The ratio of Tg to I-131 uptake was determined in four groups: Group A, tumor free (n = 81); Group B, lymph node metastases (n = 11); Group C, distant metas tases (n = 11); Group D, later recurrence [during a mean follow-up of 56 mo; (n = 8)]. Wilcoxon two-sample test was performed to determine s tatistical significance between Group A and Groups B-D. Results: Signi ficant differences in the Tg/I-131 uptake ratios (median) between Grou p A (1.0 ng/ml/%) and Groups B (3.3 ng/ml/%), C (20.2 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 rat io, observed in 14 of the 30 remaining patients, was indicative of met astases or later recurrence. Conclusion: The ratio of serum Tg to I-13 1 uptake in the thyroid bed might be used as a prognostic marker for t hyroid cancer before implementing ablation with I-131.