This massive collaborative study by the Breast Cancer Association Consortium examined nine variants implicated with breast cancer. This study showed that given a large enough population, even common breast cancer variants that have minor risk effects can be detected.

In breast cancer, there are only a few rare, highly penetrant genetic variants that result in breast cancer. They account for 25 percent of breast cancer risk passed on through families. The other 75 percent of genetic risk results from a number of common gene variants that have only small effects on their own, but in combination raise risk significantly.

To detect the effects of these variants, this large study combined data from 20 other studies to get a potential sample size of up to 18,290 cases and 22,670 controls of people of mostly European ancestry.

Some of the variants were identified indirectly by "tagging" a section of the genome where one is found. As they "travel in packs" and are passed on together, it is possible to find a certain variant by tagging its companions. The researchers estimated that one of the nine variants, CASP8, raised the risk of breast cancer by 3 percent.

More: To read an abstract of this paper on PubMed, a medical database, click here.