Table 11: BRCA1 and BRCA2 gene mutations and cancer risk

Introduction: Women who carry a BRCA1 or BRCA2 gene mutation have a greatly increased risk of getting breast and ovarian cancer. Studies, though, show a wide range of risks. It appears that women who have a BRCA1 or BRCA2 mutation have a 60 to 80 percent chance of getting breast cancer by age 70 and a 15 to 60 percent chance of getting ovarian cancer by age 70. In comparison, the average woman in the United States has, by age 70, a seven percent chance of getting breast cancer and a 0.7 percent chance of getting ovarian cancer [1]. BRCA1/2 carriers also seem to have an excess risk of colon cancer, prostate cancer (in male carriers) and some second primary cancers (new cancers that develop after a first breast cancer). However, these data are limited.

People with BRCA1 gene mutations seem to have slightly different cancer risks than those with BRCA2 mutations. However, the two groups are sometimes combined in the table below since there are so few data available on either group alone. Much of the research on genetic mutations and breast cancer risk has been done by the International Breast Cancer Linkage Consortium. This group has collected data on over 200 families worldwide. Each family has at least four family members with breast cancer.

The prevalence of a BRCA1 gene mutation in the general population is quite small (only about one in 800 women) [2]. However, women of Ashkenazi Jewish descent are at greater risk of a carrying a BRCA1/2 mutation, (about one in 40 have either a BRCA1 or BRCA2 mutation) [3].

Study selection criteria: For family based studies--those studies with more than 200 families that have four or more members with breast cancer. For population based studies—representative studies, with at least 100 breast cancer cases. For pooled analyses--studies with at least 400 families. 
 

* Confidence intervals for these risk estimates were not included in the original article.
† By age 80, cumulative risk of breast cancer increases to 58% (30-80%) for BRCA1 and 58% (38-81%) for BRCA2.
‡ By age 80, cumulative risk of a second breast cancer in the opposite breast increases to 47% (25-100%) for BRCA1 and 60% (34-92%) for BRCA2.

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Updated 09/12/09