Clinical Outcome of (131)I Therapy in Differentiated Thyroid Cancer with Preablative Thyroglobulin below 10 ng/ml

To investigate the clinical outcome of (131)I therapy in differentiated thyroid cancer (DTC) with preablative stimulated thyroglobulin (ps-Tg) below 10 ng/ml and the value of ps-Tg for predicting clinical outcome.

Totally 167 DTC patients with ps-Tg below 10 ng/ml were included and divided into three groups [excellent response (ER, n=131), acceptable response (AR, n=34), and incomplete response (IR, n=2)] according to the response to initial (131)I therapy. One-way analysis of variance, χ(2) test, and Kruskal-Wallis test were used to evaluate the statistical differences of clinicopathological features, recurrence risk, and ps-Tg value among the three groups. The ps-Tg value between ER group and non-ER group were compared by Mann-Whitney rank-sum test. The ROC curve and optimal cut-off point were analyzed to evaluate the clinical value of ps-Tg for predicting disease-free status.

There was significant difference in ps-Tg level (H=14.305, P=0.001) among three groups but not in age (F=0.831, P=0.755), sex (χ(2)=0.178, P=0.915), cervical lymph node metastases (χ(2)=1.475, P=0.478), TNM stage (H=1.063, P=0.588), and recurrence risk (H=2.947, P=0.229). The median level of ps-Tg in ER group was 2.20 ng/ml (1.10, 4.40), which was significantly lower than 4.40 ng/ml (2.70, 5.90) of non-ER groups (U=1424.50, P=0.000). Area under the ROC curve was 0.717. The cut-off value of ps-Tg was 2.35 ng/ml,with a sensitivity of 83.33%, specificity of 53.43%, and negative predictive value of 92.11%.

The serum ps-Tg value is a sensitive marker for predicting the disease-free status in DTC patients with ps-Tg below 10 ng/ml.