It Takes a Genome: How a Clash Between Our Genes and Modern Life Is Making Us Sick

Familial Breast Cancer

Only about ten percent of breast cancer runs in families, in the sense that sisters and daughters of an affected woman have elevated risk compared with the general population. Of this fraction, one-fifth can be attributed to two genes, BRCA1 and BRCA2. Women who inherit one bad copy of either of these genes have a lifetime risk of ovarian or breast cancer exceeding 85 percent: Each gene thus accounts for about 1 in every 100 cases of the disease. That is worth worrying about if you are in an affected family, but the flip side of this is that 97 percent of breast cancer has no known genetic basis.

Here and there, studies have by now implicated mutations in at least ten different genes in promoting specific cases of familial ...