In breast cancer, CSCs are usually defined by the CD44+/CD24−/low phenotype, and/or as being positive for the activity of the ALDH1 enzyme which is recognized by elevated proportion of an ALDEFLOUR+ cell population; often, elevated extent/size of tumor spheroids (mammospheres) is also considered a potential marker for enrichment of CSCs (74, 75). Here, CD44 is linked to breast cancer.