At least two types of breast cancer cells display CSC properties: 1) CD44+/CD24−/Lineage− cells, the first described CSCs, found mostly in basal-type breast cancers3; 2) Cancer cells that express higher levels of Aldehyde Dehydrogenase 1 (ALDH1+), which are present mostly in luminal breast cancers4. This evidence concerns the gene CD44 and breast cancer.