Genetics and Cancer: New Study Clarifies the Link
Breast and ovarian cancer are serious health threats to women in the U.S. Other than ]]>skin cancer]]> , ]]>breast cancer]]> is the most common cancer in American women. A woman’s risk of developing breast cancer during her lifetime is more than 10%. Although ]]>ovarian cancer]]> is more rare, with a lifetime risk of 1.8%, it is one of the most lethal forms of cancer.
While most breast and ovarian cancers occur sporadically (no clear genetic link), 5% to 10% are inherited. Researchers have linked inherited mutations in the BRCA1 and BRCA2 (short for breast cancer 1 and breast cancer 2) genes with breast and ovarian cancer.
While it is not inevitable that women with these mutations will develop cancer, they are at substantially higher risk. Previous studies have estimated the lifetime risk of breast cancer in women with mutations in BRCA1 or BRCA2 genes is more than 90%, and the lifetime risk of ovarian cancer is 40% and 20% for BRCA1 and BRCA2 carriers, respectively.
A new study in the October 24, 2003 issue of Science genetically tested the relatives of breast cancer patients carrying BRCA1 or BRCA2 mutations. The researchers found that female relatives who carried a mutation had an 82% risk of developing breast cancer and a 23% to 54% risk of develop ovarian cancer by age 80. They also found that exercise during adolescence and a healthy weight at puberty and age 21 significantly delayed the onset of cancer in these women.
About the Study
The researchers tested 1,008 women who had been diagnosed with breast cancer for mutations in BRCA1 or BRCA2 . The women were selected from the Ashkenazi (Eastern European) Jewish population, which has a relatively high percentage of easily identifiable gene mutations.
The living adult relatives of these women provided cancer histories. They were also genetically tested to determine if they carried the mutation.
The researchers gathered information about the participants’ other risk factors, including menstrual and reproductive history, exercise and body weight, contraceptive and hormone use, and environmental and occupational exposures.
Of the 1,008 breast cancer patients tested, 104 (10.3%) carried a BRCA1 or BRCA2 mutation. Compared to women without mutations, women with these mutations were more likely to develop breast cancer at a younger age, and to have a family history of breast or ovarian cancer.
Among the women with mutations, exactly half were from families with no breast or ovarian cancer among mothers, sisters, grandmothers, or aunts. In most of these low-incidence families, the mutation proved to be inherited from the woman’s father.
The risks of breast cancer in relatives who had BRCA1 or BRCA2 mutations were as follows:
- 20% by age 40
- 55% by age 60
- Greater than 80% by age 80
While both mutations increased the risk of ovarian cancer compared to the general population, BRCA1 carriers had a greater risk (54% by age 80) than BRCA2 carriers (23% by age 80).
Other interesting findings were:
Relatives who were born after 1940 had a significantly higher lifetime risk of developing breast cancer than those born before 1940.
Women who reported physical exercise as an adolescent and healthy weight at puberty and age 21 were more likely to have a delayed onset of breast cancer.
How Does This Affect You?
These findings confirm previous estimates of the high risk of breast and ovarian cancer in women with BRCA1 and BRCA2 mutations. This study also suggests that family history may not be the best predictor of inherited breast or ovarian cancer. According to these findings, screening only women with family histories of these cancers would miss half of the women with mutations.
So, should the general population be tested for these mutations? Although genetic testing for BRCA1 and BRCA2 mutations has recently become available, its use is still limited. If you are concerned about your risk of inherited breast cancer, talk to your doctor. Genetic testing may be an option for you. But keep in mind, only a small fraction of breast cancers are inherited, so your risk of having a BRCA1 or BRCA2 mutation is very low.
According to the National Cancer Institute, factors that increase your risk of having BRCA1 or BRCA2 mutations include:
- Having a family with multiple cases of breast cancer or both breast and ovarian cancer
- Having one or more family member with two primary cancers (original tumors at different sites)
- Having an Ashkenazi Jewish background
Women who find out they carry these mutations are usually referred to a genetic counselor to discuss options for preventing or delaying cancer. These options may include more frequent screening tests ( ]]>mammograms]]> , for example, every six months), preemptive ]]>mastectomies]]> (removing the breasts before cancer has a change to develop), and taking hormonal medications (e.g., tamoxifen) to reduce cancer risk. Researchers hope to eventually learn how to repair mutated BRCA1 and BRCA2 genes in people before cancer develops, but for now, prevention strategies are the best option.
The finding that women born after 1940 were at higher risk for breast cancer is difficult to explain. It does suggest, however, that the environment plays a significant role. Although this study was unable to determine the reason, it is conceivable that the widespread use of hormone replacement therapy during the past 30 years contributed to this finding.
If there’s any good news here, it is that increased physical activity and lower body weight among girls and young women may decrease breast cancer risk later in life. The message is clear: when it comes to exercise, women should do it early and often.
Breast Cancer Home Page
National Cancer Institute
National Human Genome Research Institute
Genetic testing for BRCA1 and BRCA2: it’s your choice. National Cancer Institute website. Available at: http://cis.nci.nih.gov/fact/3_62.htm .
King MC, Marks JH, and Mandell JB for the New York Breast Cancer Study Group. Breast and ovarian cancer risks due to inherited mutations in BRCA1 and BRCA2. Science Magazine . 2003;302:643–646.
Last reviewed October 31, 2003 by ]]>Richard Glickman-Simon, MD]]>
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