摘要Background Keratinocyte serum-free medium (K-SFM) is a defined medium used to support the growth of primary keratinocytes and embryonic stem cell. The aim of this research was to optimize enrichment of breast cancer stem cells (CSCs) using K-SFM.Methods A K-SFM was used to enrich CSCs from two breast cancer cell lines and a primary culture of breast cancer.RPMI-1640 supplemented with 10％ fetal calf serum (FCS) was used as a control. CSCs were identified with flow cytometry using CD44+/CD24-as molecular markers. The expression of a variety of CSC markers (Oct-4, ABCG2, Nanog,N-cadherin, and E-cadherin) was analyzed with real-time PCR.Results Much higher percentage of CSCs was achieved with K-SFM: 17.3％ for MCF-7 cells, 17.4％ for SKBR-3, and 20.0％ for primary breast cancer culture. Less than 1％ CSC was achieved using RPMI-1640 supplemented with 10％ FCS. In comparison to the CSCs obtained with RPMI-1640, CSCs in the K-SFM expressed higher levels of Oct-4,ABCG2, Nanog and N-cadherin, and lower level of E-cadherin.Conclusion K-SFM is an optimal culture medium to maintain and to enrich breast CSCs.