Current methods, such as serum thyroglobulin measurement and medical imaging, have limitations in the routine monitoring of the disease status and treatment response of patients with differentiated thyroid cancers (DTCs), and additional methods remain to be explored. The aim of this study was to investigate the clinical value of the sodium/iodide symporter (NIS) expression and epithelial-mesenchymal transition (EMT) phenotypes of circulating tumor cells (CTCs) in monitoring the disease status and treatment response of DTC. Blood samples were obtained from DTC patients before (1 to 3 months after total thyroidectomy) and 4 to 6 months after radioactive iodine-131 (RAI) therapy for the CTC assessments. The number, NIS expression, and EMT phenotypes of CTCs were enumerated and characterized with CanPatrol™ CTC enrichment and mRNA in situ hybridization. Postoperative NIS high expression was independently correlated with a better response to first RAI therapy and good treatment efficacy. Postoperative NIS-/epithelial-/mesenchymal+ CTCs presence was independently correlated with a worse response to first RAI therapy. The numbers of total NIS+ CTCs and NIS+/epithelial+/mesenchymal+ CTCs after first RAI therapy were negatively correlated with a better response to RAI therapy only in univariate analyses. Univariate and multivariate analyses showed that a decreased or unchanged number of total NIS+ CTCs after RAI therapy may denote good efficacy and effective RAI therapy. These preliminary data suggest that assessment of the NIS expression and EMT phenotypes of CTCs may serve as potential adjuncts for predicting and monitoring the curative effect of RAI therapy in DTC patients and avoid ineffective treatment. Further validation is warranted.
