Background: Breast cancer is one of the most common types of cancer in women worldwide. It has been demonstrated that even localized tumors without clinically apparent metastases give rise to circulating epithelial tumor cells (CETCs). Recent studies have provided strong support for the circulating cancer stem cell (cCSC) hypothesis, which suggests that a more aggressive subpopulation of circulating tumor cells are the source of metastatic spread from the primary tumor. Measuring CETCs in blood of patients has emerged as a non-invasive diagnostic procedure for screening patients who may be at high risk for developing metastatic cancers. However, accurate detection of CETCs may provide erroneous results, since CETCs undergoing EMT during metastasis are down-regulated for the expression of epithelial cell markers.

Methods: 26 breast cancer patients were included into the study. The determination of CETCs and cCSC was performed using maintrac® method and tumorsphere forming assay, respectively. Cell viability, surface marker expression and ALDH 1 activity of the cells in the spheres were evaluated by fluorescence scanning microscope.

Results: Sphere formation was observed in 80 % of patients. We found that the number of tumorspheres depended on stage of disease. The number of tumorspheres increased significantly with tumor progression, especially with the presence of metastases. Tumorsphere formation was observed in all metastatic patients (median of 30 tumorspheres/100μl of blood), although only 27% of them had detectable CETCs. Analysis of surface marker expression profile showed that the cells in the spheres had typical phenotype of cancer stem cells. Sphere formation was not observed in healthy subjects (n=20).

Conclusion: There is a high correlation between the numbers of tumorspheres cultured from peripheral blood with clinical stage of disease. This may be an indicator of tumor aggressiveness, especially presence of metastases and may provide clinically useful prognostic information.

Citation Format: Pizon M, Schott D, Pachmann U, Pachmann K. Detection of circulating cancer stem cells: A novel approach as a predictive marker for breast cancer metastases. This may be especially useful in patients with undetectable circulating epithelial tumor cells [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-01-12.