- J L Hopper: Department of Public Health, The University of Melbourne, Carlton, Victoria 3053, Australia. j.hopper@unimelb.edu.au
Population-based studies of the genetic epidemiology of female breast cancer have shown that only a small proportion of familial aspects of the disease can be explained by what is currently known about its causes. These include mutations in the genes BRCA1 and BRCA2, associated with a 10- to 20-fold increased risk of developing breast cancer. There may be genetic or environmental factors that modify cancer risks in mutation carriers, not necessarily in the same way as they do in non-carriers. The "typical BRCA1/2 family" consists of a "sporadic case", not a multiple-case family. There are likely to be other dominantly- and even recessively-inherited genetic risks, including those influencing intermediate markers like mammographic densities. Unravelling all the causes of familial aggregation will be a major step in understanding the causes of female breast cancer.