These interactions include ATM and CHEK2 with BRCA1 and BRCA2, ATM and BRCA, CHEK2 and BRCA1/BRCA2 combined, and CHEK2 and BRCA1 or BRCA2. The results show a lower risk of breast cancer than that predicted by the multiplicative product of the constituent risks. Here, CHEK2 is linked to breast cancer.