Baseline stimulated thyroglobulin level as a good predictor of successful ablation after adjuvant radioiodine treatment for differentiated thyroid cancers.

BACKGROUND

To determine the predictive value of the baseline stimulated thyroglobulin (STg) level for ablation outcome in patients undergoing adjuvant remnant radioiodine ablation (RRA) for differentiated thyroid carcinoma (DTC).

MATERIALS AND METHODS

This retrospective study accrued 64 patients (23 male and 41 female; mean age of 40±14 years) who had total thyroidectomy followed by RRA for DTC from January 2012 till April 2014. Patients with positive anti-Tg antibodies and distant metastasis on post-ablative whole body iodine scans (TWBIS) were excluded. Baseline STg was used to predict successful ablation (follow-up STg<2 ng/ml, negative diagnostic WBIS and negative ultrasound neck) at 7-12 months follow-up.

RESULTS

Overall, successful ablation was noted in 37 (58%) patients while ablation failed in 27 (42%). Using the ROC curve, a cut-off level of baseline STg level of ≤14.5 ng/ml was found to be most sensitive and specific for predicting successful ablation. Successful ablation was thus noted in 25/28 (89%) of patients with baseline STg≤14.5 ng/ml and 12/36 (33%) patients with baseline STg>14.5 ng/ml ((p value<0.05). Age>40 years, female gender, PTS>2 cm, papillary histopathology, positive cervical nodes and positive TWBIS were significant predictors of ablation failure.

CONCLUSIONS

We conclude that in patients with total thyroidectomy followed by I-131 ablation for DTC, the baseline STg level is a good predictor of successful ablation based on a stringent triple negative criteria (i.e. follow-up STg <2 ng/ ml, a negative DWBIS and a negative US neck).