Background: Circulating thyroid cancer cells detected by peripheral blood thyroid-stimulating hormone receptor (TSHR) mRNA have demonstrated usefulness for thyroid cancer diagnosis and long-term surveillance. The aim of this study was to determine detectability and clinical importance of TSHR mRNA in patients with microcarcinomas. Methods: We compared clinical characteristics of 37 patients with papillary thyroid microcarcinomas (PTMC; tumor size ≤1 cm) having undetectable (-) versus detectable (+)TSHR mRNA. Results: 59 Of the PTMC patients, 59% had (+)TSHR mRNA levels, similar to those with tumors >1 cm (72%; P = NS) and distinctly higher than false (+) rates in benign goiters (15%; P < .001). All patients with (-)TSHR mRNA had classical PTMC, whereas variants (32%) occurred with (+)mRNA (P = .001). Mean tumor size (5 mm) and multifocality rates (45%) were similar in both mRNA groups. Of the PTMC patients, 35% had concurrent cervical nodal metastases, which occurred more frequently with tumors ≥5 mm (P = .04) and with (+)TSHR mRNA in pre-operatively known PTMC (P < .05). No patients with incidentally detected PTMC and (-)TSHR mRNA had metastases. Conclusion: This study is the first to demonstrate that TSHR mRNA, reflecting circulating thyroid cancer cells, is detectable even with thyroid microcarcinomas. PTMC with (+)TSHR mRNA may characterize patients with potentially more aggressive histology at initial operation.
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