Microscopic Calcifications Isolated from Thyroid Fine Needle Aspiration Can Serve as Biomarkers of Thyroid Nodule Malignancy

Abstract

Thyroid nodules (TNs) are common neck ultrasonography (US) findings, yet only 5-10% of these nodules harbor thyroid cancer (TC). When US characteristics are consistent with an intermediate or high suspicion for TN malignancy, fine needle aspiration for cytology (FNAC) is indicated. The main limitation of FNAC is that cytological results can be indeterminate in up to 30% of cases, necessitating reevaluation through repeated FNAC, expensive molecular testing, or diagnostic thyroid lobe resection.  As such, there is a need for the further refinement of current diagnostic algorithms for TNs without subjecting patients to additional invasive procedures. As calcifications detected during thyroid US are considered a high-risk feature for malignancy, we used the material remaining following routine thyroid FNAC to isolate microscopic calcifications (MCs). We then characterized the elemental composition, morphology, and crystal phases of these MCs, ultimately revealing differences between the MCs from benign and malignant TNs. Specifically, thyroid MCs were identified as calcium phosphate crystals containing varying levels of magnesium, sodium, iron, and zinc. MCs obtained from malignant TNs were composed of sub-micrometer spherical particles, whereas MCs from benign TNs consisted of faceted particles. The presence of zinc in these MCs was found to differentiate between benign and malignant TNs. While samples from most patients with malignant TNs harbored zinc-containing MCs, zinc was largely absent in MCs from benign TNs. Together, these data thus suggest that the presence of zinc in MCs isolated from samples collected during routine FNAC can offer value as a biomarker of TN malignancy.

Funding Information: This work was supported by Ben-Gurion University Startup grant and the Israeli Science Foundation [grant number 565/21].

Declaration of Interests: LG, MF, UY, and NV have filed a provisional patent on this technology. DA declares that she has no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Ethics Approval Statement: Samples were collected between November 2020 and July 2022 during FNAC procedures conducted at the endocrine unit of Soroka University Medical Center (SUMC). Patients aged 18 years or older with TNs and an indication of FNAC who agreed to sign the informed consent document were included in this study. The institutional review committee approved this study in advance of its execution (approval number 190-17-SOR, 27 Sep 2017).

Keywords: biomineralization, Pathological calcification, thyroid cancer