The importance of such molecular epidemiological studies can be illustrated using the example of breast cancer. Even after researchers had identified a gene called BRCA1, which is associated with greatly increased risk of breast cancer, the implications of this gene for the breast cancer risk in the general population remained unknown for a long time because epidemiological studies were not carried out (Hopper 2001). Until such epidemiological studies were conducted, women in the general population (as well as women with a family history of breast cancer) could not be told how likely it was that if they underwent genetic testing, they would be found to have the high-risk gene.
