Epithelial cell adhesion molecule (EpCAM)high integrin subunit alpha 6 (CD49f)+ luminal progenitors (LPs) and EpCAMlow/−CD49f+ basal cells (BCs) were isolated (Figure S1a) from reduction mammoplasty samples from 3 cancer-free non-carriers or prophylactic mastectomies obtained from 3 BRCA1-mutant donors (Fig. 1a, Table S1). Here, ITGA6 is linked to cancer.