CD44 and breast cancer: Previously studies have been confirmed that breast cancer contains a CSC-compartment [11]–[13], which can be enriched by purifying Aldehyde dehydrogenase 1 (ALDH1)-positive cells [13] or CD44+/CD24−/low cells [11] by sorting, and also by purifying sphereforming cells (mammospheres) from parental cells [12].