Moreover, tetraploidy, loss of the wild-type allele at the ATM locus, and copy number loss/LOH at loci 13q14.11-q14.3, 17p13.2-p12, 21p11.2-p11.1 and 22q11.23 are hallmarks of breast tumours developed by ATM variant carriers. This evidence concerns the gene ATM and breast neoplasm.