Estimation of tumour mass in patients with differentiated thyroid carcinoma using serum thyroglobulin

Summary

Serum thyroglobulin (Tg) is a reliable tumour marker in follow-up of patients with differentiated thyroid carcinoma (DTC). A positive correlation between Tg level and tumour mass was recently observed, but no attempts were made to derive a numerical relation. The aim of this study was to derive a numerical relationship between serum Tg level and tumour mass that allows optimizing the diagnostic procedures. Patients, method: 78 DTC patients with tumour lesions in either 124I-NaI or 18F-FDG PET/CT were included. For each patient, the total tumour mass was determined functionally in iodine- and FDG-positive lesions as well as morphologically in only CTpositive lesions. The serum Tg level was measured under TSH stimulation prior to imaging. Regression analyses were performed to derive an approach for estimation of the total tumour mass based on Tg levels. Results: A positive correlation of serum Tg and tumour mass was confirmed and a mathematical expression was given to estimate the tumour mass along with its 95% confidence interval using only the serum Tg level. The results demonstrated that the range of predicted tumour mass was higher per serum Tg unit for iodinepositive lesions than for FDG-positive tumour lesions and was higher for follicular than for papillary thyroid carcinoma. Conclusion: This study provides an approach to estimate the tumour mass and its 95% confidence intervals in DTC patients using the serum Tg level. The range of the estimated tumour mass for a given Tg level is rather large, and therefore, the approach is of limited value in clinical application.

Zusammenfassung

Serum-Thyreoglobulin (Tg) ist ein verlässlicher Tumormarker in der Nachsorge des differenzierten Schilddrüsenkarzinoms (DTC). Eine positive Korrelation zwischen Tg-Konzentration und Tumormasse ist bekannt, jedoch wurde bislang keine numerische Beziehung hergestellt. Ziel dieser Studie war es, diese numerische Beziehung zwischen Serum-Tg-Konzentration und Tumormasse herzustellen, um den Einsatz von diagnostischen Modalitäten zu optimieren. Patienten, Methode: DTC-Patienten (n = 78) mit im 124I-NaI- oder 18F-FDGPET/ CT nachweisbaren Tumorläsionen wurden eingeschlossen. Für jeden Patienten wurde die komplette Tumormasse entweder funktionell aus Iod- oder FDG-positiven Tumorläsionen oder morphologisch bei nur CT-positiven Läsionen bestimmt. Die Serum-Tg-Konzentration wurde unmittelbar vor der Bildgebung unter TSH-Stimulation bestimmt. Zur Abschätzung der gesamten Tumormasse anhand der Tg-Konzentration wurden Regressionsanalysen durchgeführt. Ergebnis: Eine positive Korrelation zwischen Tg und Tumormasse konnte bestätigt werden und eine numerische Beziehung zur Abschätzung der Tumormasse sowie des 95%-Konfidenzintervalls auf der Basis des Serum-Tg-Spiegels konnte erstellt werden. Die Spannweite der errechneten Tumormasse pro Tg-Einheit war größer für rein Iod-positive Tumorläsionen im Vergleich zu rein FDG-positiven, ebenso war diese größer für follikuläre- im Vergleich zu papillären DTC. Schlussfolgerung: Diese Studie bietet eine Möglichkeit zur Abschätzung der Tumormasse und des 95%-Konfidenzintervalls anhand des Serum-Tg-Spielgels für DTC-Patienten. Die Spannbreite der abgeschätzten Tumormasse bei einem bestimmten Tg ist jedoch sehr groß, weshalb dieser Ansatz in der klinischen Routine von limitiertem Wert ist.

Keywords

Thyroid carcinoma - thyroglobulin - tumour mass - correlation

Schlüsselwörter

Schilddrüsenkrebs - Thyroglobulin - Tumor - masse - Korrelation

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