For example, a small subpopulation of cancer cells is present within some human breast cancers that exhibit a CD44 +/CD24 (−/low) phenotype; these tumorigenic cells have been shown to be highly enriched for CICs in xenografts compared to their counterparts [154], and display a mesenchymal phenotype in the invasive front of the tumor [155]. Here, CD44 is linked to breast carcinoma.