Low but measurable stimulated serum thyroglobulin levels <2 µg/L frequently predict incomplete response in differentiated thyroid cancer patients

Nomogram for the Prediction of Biochemical Incomplete Response in Papillary Thyroid Cancer Patients

Purpose

To develop a nomogram for predicting biochemical incomplete response (BIR) in the dynamic risk stratification (DRS) of papillary thyroid carcinoma (PTC) patients without structural recurrence, and to investigate its validity.

Patients and Methods

Overall, 1705 (1005 and 700 in the training and validation cohorts, respectively) PTC patients treated with total thyroidectomy without structural recurrence were included. multivariate logistic regression analyses were performed to determine the significant predictors of BIR in the training cohort. A nomogram was subsequently constructed for BIR risk prediction. Assessments for the predictive accuracy, discrimination, and calibration of the nomogram were performed. Subsequently, internal and external validations were conducted.

Results

In the multivariate analysis, age, sex, lymph node metastasis site, extrathyroidal extension, and lymphovascular invasion showed significant predictive value; using these predictive factors and tumor size, a nomogram for BIR risk prediction was constructed. In the training cohort, the nomogram showed good predictive performance and discrimination in the receiver operating characteristic (ROC) curve analysis, with an area under the curve (AUC) of 0.765. In internal validation, the bootstrap-corrected AUC was 0.76. The calibration plot showed good agreement between the predicted and actual observation. The Hosmer-Lemeshow (HL) test did not suggest a lack of fit (p=0.1613). In the external validation, the AUC was 0.828 in the ROC curve analysis; the calibration plot showed good quality, and the HL test did not suggest a lack of fit (p=0.2161).

Conclusion

The constructed nomogram may effectively predict the risk of BIR in DRS in PTC patients without structural recurrence.

Level of Evidence

Level 4.

The Use of Post-ablation Stimulated Thyroglobulin in Predicting Clinical Outcomes in Differentiated Thyroid Carcinoma - What Cut-off Values Should We Use?

AIMS

Recently published international guidelines recommended using the stimulated thyroglobulin (sTg) post-radioactive iodine (RAI) ablation, in conjunction with tumour stage, as a risk stratification factor. The choice of cut-off values for sTg, namely 1 and 10 ng/ml, was, however, largely based on the functional sensitivities of the assays used, with relatively few published data addressing the prognostic impact of alternative cut-off values. Our study aims to provide data on the prognostic value of sTg at different levels of sensitivities and specificities.

MATERIALS AND METHODS

We conducted a retrospective review of all adult cases of differentiated thyroid carcinoma receiving RAI ablation at our centre from 2008 to 2010. All patients had sTg measured at around 6 months post-ablation. The functional sensitivity of our assay was 0.5 ng/ml. The outcome was adverse clinical event, defined as cancer-related death, persistent macroscopic disease demonstrable on imaging (including radioisotope scan) and/or receiving further treatment for persistent or recurrent disease. A receiver operating characteristic (ROC) analysis was carried out.

RESULTS

We identified 140 patients treated in the review period, with 106 of them suitable for further analysis. The reasons for exclusion included the presence of anti-thyroglobulin antibodies and medullary or anaplastic histological subtypes. Most (54.7%) had intermediate-risk disease as per the American Thyroid Association classification (2009). The median follow-up duration was 6.4 years; the minimum, excluding deaths, was 5.0 years. ROC analysis showed that the optimal cut-off value of sTg for predicting adverse clinical events was >1.0 ng/ml, associated with a sensitivity of 90.9%, a specificity of 81.0%, a positive predictive value of 55.6% and a negative predictive value of 97.1%.

CONCLUSION

Based on ROC analysis of sensitivities and specificities, our data showed that a post-ablation sTg value of 1 ng/ml is the optimal cut-off in prognostication of adverse clinical events.