Abstract
An interesting article has been recently published on Annals of Nuclear Medicine [1] about risk stratification and prediction of cancer of focal thyroid fluorodeoxyglucose uptake during other cancer evaluation; among 11,623 subjects studied for oncologic purposes, 140 showed pathologic uptakes judged eligible for fine needle aspiration biopsy (FNAB). In 37 patients, a papillary thyroid carcinoma was diagnosed, while in the other 103, benign lesions were detected (mostly adenomatous goiter, thyroiditis and nodular hyperplasia) with a maximum standardised uptake value (SUV max) significantly different from a statistical point of view (p = 0.0093) between two groups, suggesting a possible role of SUV max in differentiating one type of lesions from the other. Despite the interesting scientific and statistical analyses, the very large number of patients studied and the objective to find a metabolic key to discriminate benign lesions from malignant ones, we agree and highlight the concerns reported by the authors in the current study; in particular we stress the doubts about the effective role of SUV max per se in discriminating benign from malignant thyroid lesions and this paper gets the opportunity to briefly discuss this issue. The absence of dual-time-point acquisition (already tested and reported in literature for many malignancies [2] and also for thyroid cancer in this journal [3–5]), which is potentially useful in partially overcoming the relatively low specificity of SUV max value, could further strengthen these doubts; although dual-time-point acquisition is reported to be more specific than SUV value at standard acquisition, it could be unsafe to consider SUV max per se a pivotal key in the interpretation of the nature of lesions and for the discrimination between benign and malignant. In other words, SUV per se is a semi-quantitative parameter that reflects metabolic activity but not a specific marker of malignancies; in fact many thresholds have been proposed to distinguish benign from malignant lesions but no safe cut-off, often different in dissimilar tissues and histologic types, has been identified; moreover, it is well established that inflammation and infectious diseases show very high uptake reaching SUV max and SUV mean value not significantly different from those expressed by malignant tumors [6–8]; as a result, a different grade of inflammation in a lesion could mimic, contribute or be a confounding factor in the discrimination process and differential diagnosis. Regarding thyroid nodules, the clinical and diagnostic scenario become more complicated; in fact no high-quality evidence has been reported about the usefulness of FDG-PET/CT in staging and restaging of differentiated thyroid carcinoma (DTC) but only recommendation for patients with negative I-131 scan and elevated thyroglobulin [9]; a loss of iodine uptake ability, due to decrease in energy-dependent transport mediated by the Na/I symporter (NIS) [10], is probably counterbalanced by high glucose transporter type 1 (GLUT-1) gene expression in the de-differentiation process; this is probably due to generally low glucidic metabolism of DTC, low biologic aggressiveness and favourable clinical behaviour compared with DTC I-131 negative characterised by high FDG uptake and worse prognosis; however, it is very interesting that many papers report incidental thyroid F. Bertagna (&) Department of Nuclear Medicine, Spedali Civili di Brescia, P.le Spedali Civili, 1, 25123 Brescia, Italy e-mail: francesco.bertagna@spedalicivili.brescia.it
Published Version
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