Total thyroidectomy and radioiodine ablation are the standard treatment modalities for differentiated thyroid carcinomas (DTC). Disease recurrence after these treatments can easily be detected by monitoring the serum thyroglobulin (Tg) concentrations/anti-thyroglobulin antibody (TgAb) titers and/or by radioiodine whole body scan (WBS). The aim of this study is to estimate the usefulness of FDG/PET-CT (PET) in patients with DTC after first-line treatment. We classified 265 patients with DTC treated during the last 21 years according to the serum Tg/TgAb levels, results of WBS, and presence/absence of a poorly differentiated component in the tumor, and examined the rate of performance and usefulness of PET in each group.
A total of 134 patients who were Tg-negative, TgAb-negative and WBS-negative were classified into the Biochemical Complete Remission (BCR) group, 23 patients who were Tg-negative, WBS-negative and TgAb-positive were classified into the BCR+Ab group, 66 patients who were Tg-positive and WBS-negative were classified into the Biochemical Persistent Disease (BPD) group, 16 patients in whom the tumor contained poorly differentiated components were classified into poorly differentiated group, and 15 patients with known metastatic lesions were classified into the M1 group.
The rates of performance of PET were 3%, 13%, 21%, 50% and 27% in the BCR, BCR+Ab, BPD, poorly differentiated and M1 groups, respectively. The rates of detection of recurrence in the five groups were 0%, 33%, 57%, 38% and 50%, respectively.
In the BPD group, the Tg values were significantly higher in the patients who were determined as being recurrence-positive by PET (median Tg value is 19.4 ng/ml) than in those who were determined as being recurrence-negative by PET (median Tg value is 1.35 ng/ml).
However, there were no significant differences in the Tg values between cases in the poorly differentiated group who were determined by PET as being recurrence-positive (median 0.4 ng/ml) or recurrence-negative (median 0 ng/ml).
We concluded that PET is useful for detecting recurrence in patients of the BPD, poorly differentiated, M1 and BCR+Ab groups with elevated serum TgAb titers.
