Cancer stem cells

Emerging evidence suggests that cancers contain a rare and biologically distinct subpopulation of cells with the ability to self-renew and to sustain tumor growth, termed "cancer stem cells". Cancer stem cells share many characteristics with normal stem cells including self-renewal, asymmetric division, indefinite proliferative capacity, and self-protection mechanisms. The cancer stem cell concept is best understood in hematologic malignancies. In solid tumors, breast cancer stem cells have been the most explored. Several techniques have been described, allowing the identification or isolation of cancer stem cells by either expression of specific cell surface markers, their differential ability to efflux dyes, or by a distinct enzymatic activity. More recent studies also established the crucial role of cancer stem cells in multistage cancer progression and metastasis which has important implications for the design of novel targeted therapies. Since most of the conventional chemotherapies only affect differentiated cancer cells, initial reduction in tumor mass is often followed by a rapid relapse. In order to achieve durable remissions, it will be imperative to eradicate cancer stem cells.