Our results indicate that Z is more potent to stimulate primary culture human breast cancer epithelial cells (PCHBCECS) growth than primary culture human normal breast epithelial cells (PCHNBECS) and the stimulatory effects may be mediated by regulating the expression of DNMT1 and down-regulating p53 expression in PCHBCECs but not in PCHNBECs. This evidence concerns the gene DNMT1 and breast cancer.