Growth Factors and the Risk to Populations

Turning now to the vast majority of cases where breast cancer does not run in families, we can still ask whether genes might be involved. Groups all over the world have been tackling this question from different angles for a dozen years. For the most part they have been taking educated guesses and following up suggestive leads. In 2005, a consortium of 20 of these groups decided to pool their resources and look to see whether there were any consistent results in their combined set of more than 30,000 cases of breast cancer, admittedly mostly in Caucasian women.

The outcome was somewhat humbling. Just two genes out of the nine best guesses showed a consistent association with risk of cancer. The most convincing of these is a variant of the gene CASP8, which provides a modest protection against breast cancer for about a quarter of all women. The gene is involved in getting cells to commit suicide when damage to the DNA is sensed. It is the only case we know of to date where the protective variant is the less common one, where most women are at greater risk of cancer because they have the more common flavor of genetic variation.