The ataxia-telangiectasia mutated (ATM; MIM 607585), checkpoint kinase 2 (CHEK2; MIM 604373) and v-erb-b2 avian erythroblastic leukemia viral oncogene homolog 2 (ERBB2; also named HER2; MIM 164870) genes have been suggested to have an important role in breast cancer aetiology. Here, ATM is linked to breast cancer.