Understanding why BRCA1 mutation carriers have a predilection for developing clinically aggressive basal-like breast tumors could inform the development of targeted treatment or prevention strategies. Analysis of both mouse and human mammary epithelial cells has identified a role for BRCA1 in orchestrating differentiation. The ability to isolate discrete epithelial subpopulations from mammary tissue has recently directed attention to luminal progenitor cells - the descendants of mammary stem cells - as the likely 'cells-of-origin' in BRCA1-associated breast cancer. A new publication has confirmed the importance of aberrant luminal cells as key culprits and provided insights on how BRCA1 haploinsufficiency biases luminal cells toward a basal-like fate through aberrant expression of the transcription factor SLUG
