The authors observed that as few as a hundred CD44+CD24− cells, which were further proved to be BCSCs, were able to form tumours when injected in the mammary fat pad of non-obese diabetic severe combined immunodeficient (NOD/SCID) mice, whereas a greater number of breast cancer cells with other phenotypes failed to sustain tumour growth. The gene discussed is CD44; the disease is breast carcinoma.