A mutation in the CHEK2 gene causes a 2-fold increased breast cancer risk in female heterozygous carriers. We identified patients from breast cancer families that carried a CHEK2 mutation in both alleles (homozygous). These women have a high breast cancer risk and in addition a severe phenotype with bilateral breast cancer and multiple primary tumours. To optimize breast cancer surveillance, we propose to identify these high risk patients, by testing CHEK2 mutations in familial breast cancer patients. (By Quinten Waisfisz, PhD, http://jmg.bmj.com/content/early/2011/11/05/jmedgenet-2011-100380.abstract?papetoc )