For all CBC patients we obtained germline mutation data for the DDRP genes BRCA1, BRCA2, CHEK2 and ATM. In total, we identified 51 pathogenic germline mutations in these DDRP genes among the 247 CBC patients (21%), an increase over the estimated 10% mutation carriers among all women with primary breast cancer diagnosed before the age of 50 years (estimated from mutation frequencies reported previously [1,6,15]; Table 2). Here, CHEK2 is linked to complete blood cell count.