In conclusion, isolated and sorted CD44+/CD24− breast cancer cells only temporarily preserve this phenotype and ultimately revert to an equilibrium state in which the expanded sub-population regains the original cell surface profile of the parental cell line, which was deduced because the unsorted mammospheres and the 3-week old sorted CSCs both have similar CD44+/CD24− content (33.2% and 35.5%, respectively). This evidence concerns the gene CD44 and breast cancer.