CHEK2 and breast cancer: Assuming a baseline risk of that of women between the age of 40 and 50 without a mutation and without a family history (0.26%), the relative risk associated with a CHEK2 mutation was 5.4 (95% CI 1.1 to 2.8) and that associated with a family history of breast cancer (first-degree relative) was 1.7 (95%CI 0.2 to 12).