We followed tumor development in these mice and found that 50% (n = 34) of p18mt;Gata3+/- and 30% (n = 27) of p18mt mice developed mammary tumors between 8-20 months, indicating that haploid loss of Gata3 in p18 mutant mice accelerates mammary tumorigenesis (Table 2). This evidence concerns the gene GATA3 and breast cancer.