Abstract
PurposeTo investigate the potential role of serum thyroglobulin doubling time (TgDT) in predicting 2-deoxy-2-[18F]fluoro-d-glucose ([18F]FDG) PET/CT results in patients affected by differentiated thyroid carcinoma (DTC) who demonstrated a combination of positive Tg but a negative [131I] whole-body scan ([131I]-WBS).Materials and methodsInclusion criteria were (1) prior [131I] treatment for DTC, (2) negative subsequent [131I]-WBS, (3) no interfering anti-Tg antibodies, (4) three consecutive Tg measurements under the thyroid hormone replacement therapy to calculate TgDT before 2-[18F]FDG PET/CT, and (5) at least 6 months of clinical and/or imaging follow-up to ascertain the diagnosis. Receiver operating characteristic (ROC) curve and the area under the curve (AUC) were used to identify the optimal cutoff point for the last stimulated Tg and TgDT prior to [18F]FDG PET/CT.ResultsOne hundred and thirteen patients were included. Seventy-four (65%) patients had positive [18F]FDG PET/CT for DTC recurrence, while the remaining 39 (35%) negative. Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of [18F]FDG PET/CT were 92%, 94%, 97%, 87%, and 93%. Patients with positive [18F]FDG PET/CT had higher Tg and TgDT than those with negative PET/CT. ROC curve analysis revealed an optimal Tg cutoff of 19 ng/mL (sensitivity 78%, specificity 85%, AUC = 0.844) and TgDT of 2.5 years (sensitivity 93%, specificity 87%, AUC = 0.911). TgDT threshold of 2.5 years predicted significantly (p = 0.023) better than Tg level PET/CT results.ConclusionsThe diagnostic performance of [18F]FDG PET/CT could be significantly improved when TgDT is less than or equal to 2.5 years, as compared with using the absolute Tg level.
Highlights
This article is part of the Topical Collection on EndocrinologyDifferentiated thyroid cancer (DTC) is the most frequent endocrine cancer, which is usually characterized by a favorable outcome and a long-term survival [1] in patients without distant metastases [2]
Serum thyroglobulin (Tg) is a sensitive tumor marker used in detection of residual and/or surveillance for recurrent differentiated thyroid carcinoma (DTC)
We aimed to investigate the threshold levels for Tg and thyroglobulin doubling time (TgDT) that best correlate with the [18F]FDG PET/CT diagnostic performance and compare their relative usefulness for localizing sites of non-iodine avid DTC in patients with detectable Tg but a negative [131I]-WBS
Summary
This article is part of the Topical Collection on EndocrinologyDifferentiated thyroid cancer (DTC) is the most frequent endocrine cancer, which is usually characterized by a favorable outcome and a long-term survival [1] in patients without distant metastases [2]. In case of suspected recurrence, a neck ultrasound and a diagnostic [131I] whole-body scan ([131I]-WBS) are the initial examinations for localizing and staging the disease [3], but they have some limitations. Ultrasound is an operator-dependent technique and limited to the study of cervical lymph node metastases only, while [131I]WBS is able to detect only the iodine avid DTC. The 2-deoxy2-[18F]fluoro-D-glucose positron emission tomography/ computed tomography ([18F]FDG PET/CT) is able to identify metastatic DTC throughout the body and does not rely on iodine avidity. The main indication for [18F]FDG PET/CT in DTC is to localize non-iodine avid recurrent or residual disease in patients with detectable (usually > 1.0 ng/ mL) or increasing Tg levels who had a negative [131I]-WBS and evaluation of prognosis and assessment/definition of RAI refractory disease [4,5,6]
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