BRCA1 and breast cancer: Given that the remaining wild-type Brca1 allele was lost in CK5-positive basal-like cells, not in CK5-negative cells, in Brca1 heterozygous mammary tumors [35], and that GATA3 functions downstream of BRCA1 to suppress breast cancer [32], it will be interesting to determine if LOH of Gata3 occurs in certain groups of Gata3 heterozygous mammary tumor cells.