Taking into consideration of the similar potential of p18mt;Brca1+/- and p18mt;Gata3+/- tumor cells in promoting tumor initiation and metastasis, these results indicate that in breast cancer cells Gata3 deficiency functions similarly with Brca1 deficiency in activation of EMT and promotion of tumorigenesis and metastasis. This evidence concerns the gene BRCA1 and breast cancer.