ALDH1A1 and breast cancer: Notably, our group has recently demonstrated that breast cancer cells that have in vivo metastatic capacity in mice models [41] have increased CSC activity, but most importantly, we showed that human metastatic lesions [42], specifically brain metastasis, are enriched for a BCSC phenotype (determined by CD44, integrin subunit α6, EpCAM, cadherin-3, and ALDH1 expression).