Figure 4.

Results and data herein suggest that breast cancer overall may be viewed as a hierarchal disease, consisting of a two-component mixture of two main cell types of origin (ie, luminal vs basal/myoepithelial). As hypothesized in this cartoon, human epidermal growth factor receptor 2–enriched (HER2E) and luminal intrinsic molecular subtypes are initiated (lightning bolts) from the luminal cell compartment. On the other hand, in this model, basal-like breast cancers (HER2⁻/HR⁻) are initiated within the basal/myoepithelial cell compartment.