PIK3CA and breast cancer: Pik3ca mutation in lineage-restricted mammary basal and luminal cells can both induce multipotent stem-like cells, which is followed by development of tumor heterogeneity and multilineage mammary tumors.247 Luminal progenitor cells derived from BRCA1 basal-like breast cancers have also been confirmed to undergo dedifferentiation.248,249 Mechanically, MYC plays a central role in the reprogramming of the lineage-specific cells.