The average woman (without an inherited breast cancer gene abnormality) in the United States has about a 12% risk of developing breast cancer over a 90-year life span.

In contrast, women who have an abnormal BRCA1 or BRCA2 gene have about a 60% risk of being diagnosed with breast cancer during their lifetimes, according to the National Cancer Institute.

Women with BRCA1 and BRCA2 abnormalities are also at increased risk of developing ovarian cancer. The lifetime risk is about 55% for women with BRCA1 mutations and about 25% for women with BRCA2 mutations.

By comparison, about 1.8% of women without an inherited BRCA abnormality get ovarian cancer. The risk for certain other cancers may also be higher with BRCA1 or BRCA2 mutations. But these risk increases (for cancers such skin or digestive tract) are much lower than the increases in risk for breast and ovarian cancer.

Yet despite the increased risk, it’s important to remember that not every person with an inherited BRCA1 or BRCA2 abnormality develops cancer. The risks associated with BRCA1 and BRCA2 mutations may be affected by:

• lifestyle and environmental factors
• how well other genes work with BRCA1 and BRCA2 to protect the body against cancer
• the particular abnormality in BRCA1 or BRCA2 and how it affects the proteins that are supposed to suppress cancer

Also, many people mistakenly believe that the cancers caused by inherited genetic abnormalities are more aggressive than other cancers. In fact, recent evidence suggests that a woman with an abnormal gene who develops breast or ovarian cancer may have a LESS aggressive form of the disease than women without an abnormal gene.

Abnormal BRCA genes and men’s cancer risk

Men who inherit abnormal BRCA1 or BRCA2 genes have an increased risk for male breast cancer. This risk is approximately 6% over a man’s lifetime. That’s about 80 times greater than the lifetime risk of men without BRCA1 or BRCA2 abnormalities.

Men with an abnormal BRCA1 or BRCA2 gene may also be three to seven times more likely than men without the abnormality to develop prostate cancer. Other cancer risks, such as cancer of the skin or digestive tract, may also be somewhat higher among men with BRCA1 or BRCA2 mutations. But, as with women, the risk increases for these cancers are much lower than the increase in risk for breast cancer.

Source: http://www.breastcancer.org/risk/genetic/bcrisk_abnrml_genes.jsp