Radioiodine therapy reduces the frequency of circulating tumour cells in patients with differentiated thyroid cancer

Objective The aim of the study was the quantification of circulating tumour cells (CTCs) in differentiated thyroid cancer (DTC) patients before and 6 weeks after radioiodine therapy (RIT). Context Circulating tumour cells (CTCs) were described more recently in cancer patients, mostly correlating with poor outcome and advanced metastases. Design Peripheral blood for identification and quantification of CTC before RIT or/and 6 weeks after RIT was provided by 55 DTC patients that received RIT for remnant tissue ablation. Patients 13 follicular thyroid cancer (FTC) patients, 31 papillary thyroid cancer (PTC) patients and 11 patients having the follicular variant PTC (FV-PTC) were included. Measurements Peripheral blood mononuclear cells (PBMCs) were isolated and EpCAM-positive CTCs were counted by immune fluorescent staining. Results A CTC positivity of 31.8% before RIT could be observed. Six weeks after RIT, the CTC positivity was reduced to 13.6%. Paired data at both time points of blood sampling could be gathered for n = 33 DTC patients. These patients had significantly higher CTC numbers before RIT than 6 weeks afterwards (0.27 +/- 0.47 vs 0.05 +/- 0.15, P = .0215). Additionally, significantly reduced CTC numbers were also demonstrated in pre-RIT CTC-positive patients (0.88 +/- 0.43 vs 0.05 +/- 0.16, P = .0039). Conclusion Our results indicate a reducing effect on the number of CTCs by RIT. Therefore, CTC enumeration should be considered as efficient tool for treatment monitoring during RIT.