CD44 and breast cancer: In addition, in the breast carcinomas, how to understand why the RP215-recognized IgG mainly correlated with the basal-like-origin of MDA-MB-231 of BCSC that show CD44+/CD24−/low, but not with the luminal-like breast cancer cell line MCF-7 of BCSC as well as the CD133+ or ALDH1+ BCSC.