BRCA1 and breast cancer: Also, for highly common disorders, the odds ratios needed to obtain clinically significant risks of disease are not particularly large; for instance, germline mutations in BRCA1 or BRCA2 provide only 7-fold to 9-fold increases in the odds of a woman developing breast cancer, yet result in post-test risks ranging from 49% to 57% [19] due to the high prior probability of the disease (roughly one in eight).