The plasticity of human breast carcinoma cells is more than epithelial to mesenchymal conversion

The human breast comprises three lineages: the luminal epithelial lineage, the myoepithelial lineage, and the mesenchymal lineage. It has been widely accepted that human breast neoplasia pertains only to the luminal epithelia l lineage. In recent years, however, evidence has accumulated that neoplast ic breast epithelial cells may be substantially more plastic in their diffe rentiation repertoire than previously anticipated. Thus, along with an incr easing availability of markers for the myoepithelial lineage, at least a pa rtial differentiation towards this lineage is being revealed frequently. It has also become clear that conversions towards the mesenchymal lineage act ually occur, referred to as epithelial to mesenchymal transitions. Indeed, some of the so-called myofibroblasts surrounding the tumor may have an epit helial origin rather than a mesenchymal origin. Because myoepithelial cells , epithelial to mesenchymal transition-derived cells, genuine stromal cells and myofibroblasts share common markers, we now need to define a more ambi tious set of markers to distinguish these cell types in the microenvironmen t of the tumors. This is necessary because the different microenvironments may confer different clinical outcomes. The aim of this commentary is to de scribe some of the inherent complexities in defining cellular phenotypes in the microenvironment of breast cancer and to expand wherever possible on t he implications for tumor suppression and progression.