Given the reported similarity between murine breast and prostate stem cells (Lawson et al, 2007) and the recent identification of a CD44+CD24− subpopulation of breast cancer cells that have an increased tumorigenic capacity (Al-Hajj et al, 2003), we sought to identify and characterise CD44+CD24− cells in human prostate cell lines. Here, CD24 is linked to breast carcinoma.