Tissue-based identification of stem cells and epithelial-to-mesenchymal transition in breast cancer.

Pathologists have recognized breast cancer heterogeneity for decades, but its causes were unknown. In recent years, basic science and translational studies have demonstrated that cancer stem cells contribute to the heterogeneous histologic and functional characteristics of breast cancer. Even more recently, the ability of breast epithelial cells to undergo an epithelial-to-mesenchymal transition has been linked to the acquisition of stem cells properties and enhanced tumor invasion, metastasis, and resistance to available treatments. The stem cells and cells undergoing epithelial-to-mesenchymal transition are attractive targets for therapy and breast cancer prevention. Despite current challenges, their identification in breast tissue samples would enable pathologists to discover and validate prognostic and predictive markers as well as identify markers of increased risk for breast cancer.