EGF and breast cancer: Together, these assays paved the way to dissecting signal-transduction pathways in stem cells and their progenitors which led, for example, to a better understanding of the role of Notch in normal mammary gland development and tumorigenesis [27], [28], the effect of the EGF/AKT pathway in initiating breast cancer [29], and the tumorigenic transformation process that generates breast cancer [30].