Together with the finding that mammary tumors developed in p18 deficient mice are Brca1- and Gata3-positive well-differentiated tumors (Figure 1, and Reference 7, 15, 20), these results indicate that Brca1 protects the Gata3 promoter from methylation to maintain Gata3 transcription in the suppression of mammary tumors. This evidence concerns the gene BRCA1 and breast cancer.