Response to Letter to the Editor: Thyroid nodules with indeterminate cytology: is it safe to say ‘thyroidectomy can be excluded if 18F-FDG-PET suggests benignity’?

in Endocrine-Related Cancer
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  • 1 Santa Casa de Belo Horizonte, Belo Horizonte, Minas Gerais, Brazil

Correspondence should be addressed to P W Rosario: pedrowsrosario@gmail.com

Dear Editor,

We thank Qichang and Bin for the comments regarding our review ‘Usefulness of accessible imaging methods in thyroid nodules with indeterminate cytology’ (Rosário et al. 2021), published in this issue of Endocrine-Related Cancer pages L1–L2.

Regarding the preference for 18FDG-PET/CT, we do not disagree. We do not provide details on this imaging method because its protocol should follow that recommended in the EANM/SNMMI guideline (Giovanella et al. 2019).

Qichang and Bin cite two sentences with which they disagree. Although we do not disagree, the statement that ‘A nodule characterized by low or absent 18FDG uptake is considered at a very low RoM’ was mentioned by us as the conclusion reached by the EANM/SNMMI guideline. The sentence ‘thyroidectomy can be excluded if these tests suggest benignity’ in fact refers to molecular tests that could still be obtained in some nodules with 18FDG uptake; let us see the full sentence: ‘Depending on the clinical context (considering pre-test RoM and maximum SUV) and availability of molecular tests, a positive 18FDG-PET scan does not necessarily represent an indication for surgery. The patient can still be submitted to molecular tests and thyroidectomy can be excluded if these tests suggest benignity’.

Our conclusion regarding 18FDG-PET in thyroid nodules with indeterminate cytology seems to be clear: ‘In the case of nodules that are not very suspicious on US, 18FDG-PET can be obtained and, if it does not reveal nodular uptake, the risk of the nodule corresponding to a macrocarcinoma is sufficiently low to allow follow-up’. First, we recommend this imaging method for nodules without a high RoM. Second, we consider 18FDG-PET to be negative in the absence of uptake; thus, the sensitivity is higher, 84–88% according to the meta-analysis cited by Qichang and Bin (Qichang et al. 2020). Within this context, the meta-analysis estimated a negative predictive value (NPV) of 92–97%. Third, we consider it important that the method detects malignant and clinically relevant (>1 cm) tumors since nodules <1 cm would not have an indication for FNA (Haugen et al. 2016). Since some false-negative cases of 18FDG-PET were microcarcinomas and tumors of uncertain malignant potential or borderline, its sensitivity and NPV would be even higher when only macrocarcinomas were considered.

Even assuming the NPV of 92–97% estimated by the meta-analysis, we do not think that the difference between this value and the NPV considered acceptable for a molecular test ruling out the need for surgery (≥94%) (Vargas-Salas et al. 2018) is clinically significant. In addition, we do not agree that any nodule with a RoM above this percentage of approximately 5% does necessarily have an indication for surgery and cannot be followed up.

Declaration of interest

The author declares that there is no conflict of interest that could be perceived as prejudicing the impartiality of this article.

Funding

This work did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.

References

  • Giovanella L, Avram AM, Iakovou I, Kwak J, Lawson SA, Lulaj E, Luster M, Piccardo A, Schmidt M & Tulchinsky M et al. 2019 EANM practice guideline/SNMMI procedure standard for RAIU and thyroid scintigraphy. European Journal of Nuclear Medicine & Molecular Imaging 46 25142525. (https://doi.org/10.1007/s00259-019-04472-8)

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  • Haugen BR, Alexander EK, Bible KC, Doherty GM, Mandel SJ, Nikiforov YE, Pacini F, Randolph GW, Sawka AM & Schlumberger M et al. 2016 2015 American Thyroid Association Management Guidelines for adult patients with thyroid nodules and differentiated thyroid cancer: the American Thyroid Association Guidelines task force on thyroid nodules and differentiated thyroid cancer. Thyroid 26 1133. (https://doi.org/10.1089/thy.2015.0020)

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  • Qichang W, Jinming S, Lu L, Bin J, Renjie W & Xiuying Z 2020 Comparison of 18F-FDG-PET and 18F-FDG-PET/CT for the diagnostic performance in thyroid nodules with indeterminate cytology: a meta-analysis. Medicine 99 e20446. (https://doi.org/10.1097/MD.0000000000020446)

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  • Rosario PW, Rocha TG & Mourão GF 2021 Usefulness of accessible imaging methods in thyroid nodules with indeterminate cytology. Endocrine-Related Cancer 28 R1R9. (https://doi.org/10.1530/ERC-20-0326)

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  • Vargas-Salas S, Martínez JR, Urra S, Domínguez JM, Mena N, Uslar T, Lagos M, Henríquez M & González HE 2018 Genetic testing for indeterminate thyroid cytology: review and meta-analysis. Endocrine-Related Cancer 25 R163R177. (https://doi.org/10.1530/ERC-17-0405)

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  • Giovanella L, Avram AM, Iakovou I, Kwak J, Lawson SA, Lulaj E, Luster M, Piccardo A, Schmidt M & Tulchinsky M et al. 2019 EANM practice guideline/SNMMI procedure standard for RAIU and thyroid scintigraphy. European Journal of Nuclear Medicine & Molecular Imaging 46 25142525. (https://doi.org/10.1007/s00259-019-04472-8)

    • Search Google Scholar
    • Export Citation
  • Haugen BR, Alexander EK, Bible KC, Doherty GM, Mandel SJ, Nikiforov YE, Pacini F, Randolph GW, Sawka AM & Schlumberger M et al. 2016 2015 American Thyroid Association Management Guidelines for adult patients with thyroid nodules and differentiated thyroid cancer: the American Thyroid Association Guidelines task force on thyroid nodules and differentiated thyroid cancer. Thyroid 26 1133. (https://doi.org/10.1089/thy.2015.0020)

    • Search Google Scholar
    • Export Citation
  • Qichang W, Jinming S, Lu L, Bin J, Renjie W & Xiuying Z 2020 Comparison of 18F-FDG-PET and 18F-FDG-PET/CT for the diagnostic performance in thyroid nodules with indeterminate cytology: a meta-analysis. Medicine 99 e20446. (https://doi.org/10.1097/MD.0000000000020446)

    • Search Google Scholar
    • Export Citation
  • Rosario PW, Rocha TG & Mourão GF 2021 Usefulness of accessible imaging methods in thyroid nodules with indeterminate cytology. Endocrine-Related Cancer 28 R1R9. (https://doi.org/10.1530/ERC-20-0326)

    • Search Google Scholar
    • Export Citation
  • Vargas-Salas S, Martínez JR, Urra S, Domínguez JM, Mena N, Uslar T, Lagos M, Henríquez M & González HE 2018 Genetic testing for indeterminate thyroid cytology: review and meta-analysis. Endocrine-Related Cancer 25 R163R177. (https://doi.org/10.1530/ERC-17-0405)

    • Search Google Scholar
    • Export Citation