Correlation Between Thyroglobulin Levels before Radioactive Iodine Therapy and the ATA Ongoing Risk Stratification after 1 Year in Patients with Differentiated Thyroid Cancer

Program: Abstracts - Orals, Poster Previews, and Posters
Session: SAT 270-310-Thyroid Neoplasia (posters)
Clinical/Translational
Saturday, April 2, 2016: 1:15 PM-3:15 PM
Exhibit/Poster Hall (BCEC)

Poster Board SAT 298
Leonardo Bandeira*, Ana Luiza Trevizani Ticly, Adriano Namo Cury, Nilza Maria Scalissi, Marilia Martins Marone, Rosalia de Prado Padovani and Carolina Ferraz
Irmandade da Santa Casa de Misericordia de Sao Paulo, Sao Paulo, Brazil
Introduction: Usually, the initial treatment of differentiated thyroid carcinoma (DTC) includes total thyroidectomy (TT) and radioactive iodine therapy (RIT). The stimulated thyroglobulin (sTg) level, after surgery and before RIT, has been considered a prognostic indicator of persistence / recurrence and remission disease. In order to optimize the follow-up, an ongoing risk stratification has been developed. In according to this classification, the patient is reclassified periodically as having an excellent (ER), acceptable (RA) or incomplete response (IR) to initial treatment. Based on the response, the follow up is established. Therefore, the first end point of this study is to assess the correlation between sTg levels before RIT and the ongoing risk stratification 1 year after dose. The second end point is to establish the utility of Tg at this moment as an independent predictor of the response to therapy in patients with DTC.

Methods: A retrospective study that assessed patients with DTC undergoing RIT after TT. The sTg levels after TT and before RIT were correlated with the ongoing risk stratification 1 year after RIT. Nonparametric Kruskal-Wallis and Mann-Whitney tests were used. ROC curve analysis was performed in order to find a cutoff level of sTg before RIT that can be considered a good predictor of response to initial treatment.

Results: Fifty six patients have been enrolled (mean age 44.7±14.4 years), most of them had papillary carcinoma (80.7%). Regarding the TNM staging 51.8% was classified as stage I, 3.6% stage II, 28.6% stage III and 16.1% stage IV while according the ATA staging 14.3% was at a low risk, 69.6% intermediate risk and 16.1% high risk of recurrence. The mean Tg levels before RIT was 6.4±13.8 ng/ml. Most patients (67.3%) had an excellent response after 1 year of treatment while 15.4% had an acceptable and 17.3% had an incomplete response. Patients with ER had a mean Tg=2.1±3.3 ng/ml, those with AR had a mean Tg=8.2±9.2 ng/mL and patients with IR had a mean Tg=22.4±28.3 ng/mL. We found a statistical significance difference among the 3 ongoing risk stratification groups regarding the Tg levels before RIT (p=0.01). This difference was observed comparing the groups ER vs. IR (p=0.009), but not ER vs. AR and IR vs. AR. The ROC curve analysis showed an area under the curve of 0.779 assuming a Tg value of 3 ng/ml.

Conclusion: We found a correlation between sTg before RIT and the ongoing risk stratification proposed by ATA. It is suggested that the higher the Tg, the greater the likelihood of an incomplete response to the initial treatment. In the literature, the Tg cutoff greater than 10 ng / ml is a major predictor of a negative response to treatment, despite having a higher specificity and reduced sensitivity. In this study, we found that a 3 ng/ml cutoff has higher sensitivity and acceptable specificity (85%) and can be a good predictor of response to initial treatment in patients with DTC.

Nothing to Disclose: LB, ALTT, ANC, NMS, MMM, RDPP, CF

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