Tumorigenic cells display unique surface marker patterns, such as CD44+ in head and neck squamous cell carcinoma (Prince et al, 2007), epithelial cell adhesion molecule (EPCAM)high CD44+ in colon cancer (Dalerba et al, 2007), CD44+ integrinα2β1+ in prostate cancer cells (Patrawala et al, 2007), CD44+ CD24−/low epithelial-specific antigen (ESA)+ (Al-Hajj et al, 2003), CD44+ CD24−/low (Ponti et al, 2005) in breast cancer associated with distant metastasis (Abraham et al, 2005), and CD44+ CD24+ ESA+ in pancreatic cancer (Li et al, 2007). Here, CD44 is linked to breast cancer.