In order to address whether the introduced BRCA1 (Tyr856His) would interfere with tumor suppressor function of wt-BRCA1 in the cells concerning to their cellular proliferation, we then compared the growth rates of breast cancer cells with BRCA1 (Tyr856His) induction with the parental wt-BRCA1 expressing cells. The gene discussed is BRCA1; the disease is breast cancer.