ABSTRACT
OBJECTIVE: To investigate the usefulness of whole body scan (WBS) and serum thyroglobulin (Tg) measurement after thyroxine withdrawal during sequential follow-ups in patients with differentiated thyroid cancer (DTC). DESIGN: Two hundred and sixty-five consecutive DTC patients were enrolled. They were previously treated with near-total thyroidectomy and I-131 remnant ablation, without initial metastases or Tg antibodies. All had the first follow-up WBS and serum Tg measurement 6-12 months after initial treatment, and 165 patients received the second follow-up without further therapy. Positive/negative predictive values (PPV/NPV) were calculated by the outcome of patients being followed up for more than 8 years (mean+/-SD: 133+/-26 months). RESULTS: Serum Tg levels while the patients were off thyroxine therapy decreased spontaneously in 39.3% of the cases without further therapy. The NPV of the first follow-up serum Tg level was excellent: <2 microg/L and <0.5 microg/L were 95.1% and 98.2%, respectively. However, the PPV of the first follow-up serum Tg level was low: >10 microg/L and 2-10 microg/L were 40% and 9.6%, respectively. The trend of Tg levels was more informative; the PPV was 62.5% in cases with an increase of serum Tg of >10 microg/L and 16.6% with an increase of <5 microg/L. However, decreasing Tg levels may associate with rapid deterioration of disease, in which cases decrease of Tg indicated dedifferentiation of the tumor. The diagnostic WBS showed the same picture in 91.5% of the patients. Only one patient (0.6%) turned from negative study to positive during the follow-up. In the meanwhile his serum Tg levels increased from 0.56 to 13.6 microg/L. CONCLUSION: It is most informative when both the trend and the levels of Tg during sequential follow-up are considered. The diagnostic WBS may be performed for selected patients with indication based on Tg levels to localize the disease.
