Short-term outcome of differentiated thyroid cancer patients receiving a second iodine-131 therapy on the basis of a detectable serum thyroglobulin level after initial treatment

The aim of this study was to evaluate the usefulness of high-dose ¹³¹I therapy administered only on the basis of raised serum Tg levels.

Among patients treated with total or near-total thyroidectomy and ¹³¹I ablation, 76 (54 women and 22 men) with differentiated thyroid cancer (41 with follicular and 35 with papillary cancer) showed a detectable (i.e. >1.5 ng/ml) serum Tg level on l-thyroxine therapy during follow-up and were included in the study. In these patients, a further ¹³¹I therapy was scheduled (range 3.7–9.25 GBq, mean 6.087±1.705). Five to seven days after this radioiodine therapy, patients underwent ¹³¹I post-therapy whole-body scan (¹³¹I t-WBS). The serum Tg value at 12 months after ¹³¹I therapy was evaluated as an indicator of short-term response to radioiodine.

At evaluation after 12 months, 21 (27.6%) of the 76 patients had a Tg value ≤1.5 ng/ml, 12 (15.8%) showed a Tg decrease of at least 50%, 22 (29%) had only a minor decrease in Tg (<50%) and 21 (27.6%) did not show any decrease in Tg. ¹³¹I t-WBS was positive in 52 patients (68%, group A) and negative in 24 (32%, group B). Normalisation of Tg was observed in 15 patients (29%) of group A and in six patients (25%) of group B. Overall, 23 (44%) patients of group A and ten (42%) of group B showed a ≥50% decrease in the Tg. Of the 52 patients of group A, 19 (36%) had local recurrence at ¹³¹I t-WBS, 18 (35%) showed lung involvement and 15, (29%) bone metastasis. On a patient basis, two (13%) of 15 patients with bone metastases, six (33%) of 18 patients with lung involvement and seven (37%) of 19 patients with local recurrence had Tg values at follow-up of ≤1.5 ng/ml (p NS). Overall, seven (37%) patients with local recurrence, eight (44%) with lung involvement and eight (53%) with bone metastases showed a ≥50% decrease in Tg.

The findings of the present study suggest that the administration of therapeutic ¹³¹I only on the basis of elevated Tg levels has a definite therapeutic effect, at least in the short term. In addition, the possibility of obtaining a post-therapeutic ¹³¹I WBS can lead to better strategy definition for these patients.