Stem cells in human breast cancer

Abstract

Increasing data support cancer as a stem cell-based disease. Cancer stem cells (CSCs) have beenfound in different human cancers, and recent evidenceindicates that breast cancer originates from and ismaintained by its own CSCs, as well as the normalmammary gland. Mammary stem cells and breast CSCshave been identified and purified in in vitroculturesystems, transplantation assays and/or by cell surfaceantigen identification. Cell surface markers enable thefunctional isolation of stem cells that can initiate andpropagate tumorigenesis in mammary gland. Theseobservations have dramatic biological and clinicalsignificance due to increasing evidence suggesting thatthe recurrence of human cancer and treatment failuremay reflect the intrinsic quiescence and drug resistanceof CSCs. Thus, the CSC hypothesis providesfundamental implications for understanding breastcarcinogenesis and for developing new strategies forbreast cancer prevention and therapy for advanceddisease. Further strategies to isolate breast CSCs, to findadditional trustworthy surface markers, and to comparegene expression pathways profiles with their normalstem cells counterparts are necessary to more accuratelydefine putative breast cell-lineage markers for thedifferent cell types present in the mature mammarygland and to identify potential therapeutical targets inbreast cancer. This review discusses the currentknowledge about stem cells and CSCs, focusing onmammary stem cells and breast CSCs, and theirconsequences for breast tumorigenesis and implicationsfor breast cancer susceptibility, prognosis, and treatment.