Objective: Previous studies have shown a high rate of visualization of uptake and a decrease in serum thyroglobulin (Tg) after therapeutic doses of 131I in well-differentiated thyroid cancer patients with elevated thyroglobulinaemia but negative diagnostic 131I whole-body scan (DxWBS), but its therapeutic effect remains controversial. We evaluate the effect of therapeutic doses of 131I in patients with elevated thyroglobulin level but negative DxWBS.
Design: Among papillary thyroid carcinoma patients who underwent total or near-total thyroidectomy and remnant ablation with radioiodine during 1996 to 2000 in our hospital, the patients who showed elevated serum Tg levels and no abnormal uptake in DxWBS were selected. The selection for treatment or no treatment was decided according to the preference of the patients, considering side-effects of therapeutic doses of 131I, and the patients were thereafter studied retrospectively.
Patients: Sixty papillary thyroid carcinoma patients with elevated thyroglobulinaemia but negative DxWBS were included. Twenty-eight patients were treated, and 32 were untreated.
Measurements: We compared serum Tg levels measured at less than 3 months before the administration of therapeutic doses of 131I or DxWBS with the levels at 6-12 months after administration between two groups. Comparable data on changes in serum Tg levels during TSH suppression (Tg-on) and those in hypothyroid phase (Tg-off) were available in 25 and 49 patients, respectively.
Results: Percentage decreases in both Tg-on and Tg-off levels of the treated group [41.2 (10.1-94.1)% and 37.0 (-176.6-88.4)%, respectively] were significantly higher than those of the untreated group [-43.6 (-180.1-7.3)% and -66.6 (-10644.2-39.1)%, respectively] (P < 0.001). The treated patients were followed-up for 23.8 +/- 19.6 months after the administration of therapeutic doses of 131I. In four cases, serum Tg levels converted to negative (< 1.0 ng/ml) both on and off T4 15-22 months after the administration of therapeutic doses of 131I, and negative serum Tg levels persisted for 24-70 months. However, negative conversion of elevated serum Tg levels was not observed in any of the untreated group. Post-treatment WBS revealed pathologic uptake in 12 of 28 cases (42.9%).
Conclusions: This study revealed that the administration of therapeutic doses of 131I has a therapeutic effect, at least for palliation in short-term observation, considering the serum Tg level as an index of tumour burden, and that it can disclose previously undiagnosed lesion in some patients with differentiated thyroid cancer who show elevated thyroglobulin level but negative diagnostic 131I whole-body scan.