The 3–4% CD44+CD24low+ cells present in all of 18 orthotopic tumours generated from CD44+CD24neg-enriched cells may reflect the lack of purity in the initial sorted cells injected (4% CD24low present in the CD24neg enriched population) or could represent phenotypic conversion within a cancer population from a lower to a greater self-renewal potential (discussed further below). This evidence concerns the gene CD44 and cancer.