CD44 and breast neoplasm: Using cells from primary breast tumors and metastatic pleural effusions, they demonstrated that as few as a hundred cells expressing the adhesion molecule CD44, the epithelial surface antigen (ESA), and did not express CD24 (a ligand for P-selectin) or it was low-expressed (ESA+/CD44+/CD24−/low) were able to sustain growth when injected into mammary fat pads of non-obese diabetic severe combined immunodeficient (NOD/SCID) immunocompromised mice [33].