ABSTRACT
A family history of breast cancer is one of the most well-established risk factors for the
disease. It has been recognized for hundreds of years that the disease can occur in an
unusually high frequency in some families. Such anecdotal evidence of familial
aggregation has been supported by many systematic epidemiological studies, showing
that breast cancer is about twice as common in the women with an affected relative with
the disease than it is in the general population (1). Since the mid-1990s, some of the genes
that underlie this familial clustering of breast cancer have been identified, and testing for
mutations in these genes is now an important part of clinical cancer genetics.
