The incidence of breast cancer is increasing, especially in older women, but the cause of the increase is not known. A guide to the screening or assessment of women who have breast complaints can come from knowledge of which groups are at greatest risk for the development of breast cancer.
Many variables acting together appear to determine whether breast cancer develops in an individual.
The BRCA1 and the BRCA2 genes, when mutated within the germ line, are associated with an approximately 85 percent risk of breast cancer development in the lifetime of individuals with such a mutation. Those with the BRCA1 mutation are also at high risk for ovarian cancer. A specific mutation within the BRCA1 gene, called l85delAG, is found in as many as one percent of Ashkenazi Jewish individuals. The BRCA1 gene encodes a large protein that may be excreted from cells and appears to control cell proliferation. Whereas perhaps only eight percent of all breast cancers can be attributed to these two genes, it is likely that other genetic defects will be found in families in which cancer of the breast and ovary are prevalent.