Assessment of SOX2 performance as a marker for circulating cancer stem-like cells (CCSCs) identification in advanced breast cancer patients using CytoTrack system

Background Recent studies have highlighted that one of the main drivers for metastatic formation and resistance to the therapy are circulating tumor cells (CTCs) and cancer stem-like cells (CSCs). Measuring the CTCs has emerged as a non-invasive procedure for selecting the patients with higher risk of progression/relapse. However, still there are no methods enabling the identification of stem-like phenotype of the CTCs. Methods The image-based method was used for the identification of the circulating cancer stem-like cells (CCSCs) in metastatic breast cancer patients. The method was optimized using the CSCs established in the mammosphere culture of MCF-7 cells. Next the protocol was implemented to identify the CCSCs in samples collected from 60 patients. Results The recovery ratio for CCSCs identification using the established method was ∼60%. The CCSCs were identified as rare events accruing only in 2 patients out of 60, who participated in the study. Interestingly, the CCSCs were found only in CTC clusters. The analysis of SOX2 expression in formalin-fixed, paraffin-embedded material, revealed that the SOX2 expression was present in primary tumor samples. Conclusion The CCSCs presence was found to be a very rare event. The obtained results suggest that the CCSCs are mainly present in CTC clusters and stem-like reprograming of the cancer cells might occur early, in the primary tumor.