CHEK2 and breast cancer: More recently, to define the tumor-suppressive function of the DDR in mammary tumor mouse model, Petrini and colleagues utilized, the same somatic ErbB2-induced mammary tumor mouse model, in combination with mutant mouse strains for a panel of genes coding for components of the DDR, such as Mre11ATDL/ATDL, Nbs1DB/DB, Chk2−/−, Nbs1DC/DCChk2−/−, p53515C/515C, p53−/− and p53BP1−/−, each of which shows defects in checkpoints activation, apoptosis and/or DNA repair [50].