Detection and prognostic significance of circulating tumor cells in patients with metastatic thyroid cancer

Context: Individual patient prognostication for advanced thyroid cancer (TC) is challenging. Circulating tumor cells (CTCs) have been shown to be a valuable prognostic marker for other solid cancers. Objective: We hypothesized that CTCs are present in the blood of patients with advanced TC and their number can predict overall survival (OS). Setting: This is a prospective study at a tertiary cancer hospital. Patients, Interventions, and Main Outcome Measures: Initial studies were performed with TC cell lines to determine the feasibility of detection using the Veridex CellSearch. CTC enumeration was performed in blood samples from 18 patients with distantly metastatic medullary TC (metMTC), 14 with distantly metastatic differentiated TC (metDTC), and 10 controls with a history of TC but no evidence of disease. The prognostic value of CTC levels to predict OS in metMTC patients was assessed. Results: CellSearch detected cells from MTC and DTC but not anaplastic TC cell lines. Six metMTC patients but no metDTC or control patients had more than or equal to 5 CTCs detected by the CellSearch assay. Median survival in metMTC patients with more than or equal to 5 CTCs was 13 months vs 51.5 months for those with less than 5 CTCs (P = .0116). The hazard ratio for mortality of patients with more than or equal to 5 CTCs compared with those with less than 5 CTCs was 3.95 (1.20-13.0, P = .0245). Conclusions: The presence of more than or equal to 5 CTCs in patients with metMTC is associated with worse OS. Larger cohorts are required to validate the prognostic value of CTC enumeration.