To determine if this is the case, we examined here the expression of CD24 during autochthonous tumorigenesis in the mouse mammary tumor virus-polyoma middle T (MMTV-PyMT) and adenomatous polyposis coli (Apc1572T/+) genetic mouse models of breast cancer, as well as in the transgenic adenocarcinoma of mouse prostate (TRAMP) cancer model, and determined the effect of CD24 deficiency on tumorigenesis in these models. This evidence concerns the gene CD24 and breast cancer.