CD44 and breast cancer: MaCSCs are enriched in the triple-negative subgroup of breast cancer and are thought to contribute to the aggressive behavior of these cancers.47, 48, 49 Similar to human and murine mammary carcinoma cells displaying high ALDH activity,11, 50, 51, 52 MDA-MB-231 TNBC cells displaying the P+/E+ surface marker profile represent TICs.12 For SUM159PT cells, CD44+/CD24-/ESA+ subset was previously identified as TICs.53 As the P+ phenotype is a surrogate for the CD44+/CD24- profile, the P+/E+ SUM159PT cells are likely to represent MaCSCs.10