18 F-FDG-PET/CT indication in patients affected by differentiated thyroid cancer with elevated serum thyroglobulin and n
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LETTER TO THE EDITOR
18
F-FDG-PET/CT indication in patients affected by differentiated thyroid cancer with elevated serum thyroglobulin and negative whole-body scanning after therapy with 131I Pedro Weslley Rosario 1 Received: 21 August 2020 / Accepted: 11 September 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Dear Sir, I read with interest the article by Albano et al. [1], which addresses the criteria for 18F-FDG-PET/TC indication for localization of the tumor in patients with differentiated thyroid carcinoma (DTC) treated with 131I, whose post-therapy whole-body scan (RxWBS) was negative and who continue to show elevated thyroglobulin (Tg) after initial therapy. Although not a criterion for inclusion in the study [1], I could complete this scenario of potential 18F-FDG-PET/CT indication by adding the absence of clinically apparent disease and absence on neck ultrasonography (US), as this method is routinely recommended for initial assessment [2–5]. A careful indication of 18F-FDG-PET/CT is indeed desirable considering its limited availability in many centers, its high costs, and the possibility of false-positive results. Within this context, instead of its immediate indication, the unstimulated Tg (u-Tg) may be monitored and 18F-FDG-PET/ CT would be reserved for patients who eventually progress with a significant increase in the tumor marker. According to the hypothesis of Albano et al. [1], this management could help to define after at least three consecutive measurements of u-Tg, with calculation of the doubling time of Tg (DT-Tg). If this time is < 2.5 years, 18F-FDG-PET/CT would be indicated. My concern is that the diagnosis and consequent therapy will be delayed in patients who already have a detectable tumor upon initial assessment. As we are talking about patients without US abnormalities, if the disease is present, many are expected to have distant metastases, as shown in the study of Albano et al. [1]. In this situation, it is reasonable to imagine This article is part of the Topical Collection on Endocrinology * Pedro Weslley Rosario [email protected] 1
Instituto de Ensino e Pesquisa da Santa Casa de Belo Horizonte, Santa Casa de Belo Horizonte, Rua Domingos Vieira, 590, Santa Efigênia, Belo Horizonte, Minas Gerais CEP 30150-240, Brazil
that the delay in diagnosis and treatment may have an impact on the prognosis. Since we are also referring to patients whose initial RxWBS was negative, it is likely that many metastases, when present, do not take up iodine, and early intervention with other therapies is therefore important. I thus consider that the hypothesis of Albano et al. [1] for the indication of 18FFDG-PET/CT in patients with elevated Tg and no apparent disease after initial therapy with 131I should highlight some patient subgroups and be applied in a more limited manner. First, there is a consensus that high-risk patients for persistent/recurrent disease should be submitted to 18F-FDGPET/CT in case of the scenario described in the first paragraph [2–5]. Unfortunat
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