Cancer stem cells in breast cancer and metastasis

The cancer stem cell theory poses that cancers\ud develop from a subset of malignant cells that possess stem\ud cell characteristics and has been proposed to account for\ud the development of a variety of malignancies, including\ud breast cancer. These cancer stem cells (CSC) possess\ud characteristics of both stem cells and cancer cells, in that\ud they have the properties of self-renewal, asymmetric cell\ud division, resistance to apoptosis, independent growth, tumourigenicity\ud and metastatic potential. A CSC origin for\ud breast cancer can neatly explain both the heterogeneity of\ud breast cancers and the relapse of the tumours after treatment.\ud However, many reports on CSC in the breast are\ud contradictory. There is variation with respect to how breast\ud cancer stem cells should be identified, their characteristics\ud and a possible lack of correlation between clinical outcome\ud and breast cancer stem cell status of a tumour. These\ud combined factors have made breast cancer stem cells a\ud highly contentious issue. In this review, we highlight the\ud progress in the analysis of cancer stem cells, with an\ud emphasis on breast cancer