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Research Brings More Information on Breast Cancer Genetics

What are the BRCA1 and BRCA2 genes?

In 1990, DNA linkage studies on large families with a certain group of characteristics identified the first gene associated with breast cancer.

Scientists named this gene “breast cancer 1” or BRCA1 (pronounced brak-uh). BRCA1 is located on chromosome 17. Mutations in the gene are transmitted in an autosomal dominant pattern in a family.

Since it was clear that not all breast cancer families were linked to BRCA1, studies continued and in 1994, scientists discovered another gene (similar to BRCA1), and named it BRCA2. BRCA2 is located on chromosome 13. Mutations in this gene are also transmitted in an autosomal dominant pattern in a family.

Both BRCA1 and BRCA2 are tumor suppressor genes that usually have the job of controlling cell growth and cell death. Everyone has two BRCA1 genes (one on each chromosome #17) and two BRCA2 genes (one on each chromosome #13).

When a person has one altered or mutated copy of either the BRCA1 or BRCA2 gene, their risk for various types of cancer increases.

Both copies of a tumor suppressor gene must be altered or mutated before a person will develop cancer.

Some individuals who have inherited a germline BRCA1 or BRCA2 mutation never develop cancer because they never get the second mutation necessary to knock out the function of the gene and start the process of tumor formation. This can make the cancer appear to skip generations in a family, when, in reality, the mutation is present.

Persons with a mutation, regardless of whether they develop cancer, however, have a 50/50 chance to pass the mutation on to the next generation.

It is also important to remember that the BRCA1 and BRCA2 genes are not located on the sex chromosomes. Therefore, mutations can be inherited from the mother or the father’s side of the family.

Always consult your physician for more information.

< Aug. 16, 2006 > -- A new study reported in the journal Cancer Research reveals the most comprehensive view to date of the prevalence in the US population of mutations in two genes associated with an increased risk of breast cancer.

In particular, the BRCA1 and BRCA2 mutations were found overall to be as common in African-American women as in Caucasian women, according to the new findings, even though the BRCA1 mutation is still much more common among Jewish women.

The study also provides the first direct evidence that women who are diagnosed with breast cancer later in life can also be carriers of the mutations.

Gene Mutations Connected to Breast Cancer

BRCA1 and BRCA2 mutations are responsible for the majority of breast and ovarian cancers in families with high-risk profiles. Some 36 percent to 85 percent of women with the mutation will develop breast cancer, and of those that do, there is also a risk of developing ovarian cancer.

Researchers have accumulated a wealth of knowledge about BRCA1 and BRCA2 in high-risk families, but know relatively little about the prevalence of the mutations in the general population, especially among African-American women and older women.

The authors of the new study looked at the prevalence of BRCA1 and BRCA2 mutations in 1,628 women with breast cancer and 674 women without breast cancer.

The women, aged 35 to 64, were participants in the National Institute of Child Health and Human Development's Women's Contraceptive and Reproductive Experiences (CARE) Study, and were from the Seattle, Los Angeles, Atlanta, Detroit, and Philadelphia metropolitan areas.

Among those with breast cancer, 2.4 percent and 2.3 percent carried mutations in the BRCA1 and BRCA2 genes respectively. About 2 percent of women who were aged 60 to 64 at the time of diagnosis were mutation carriers.

Among those without breast cancer, BRCA1 mutations were found in 0.04 percent, and BRCA2 mutations in 0.4 percent.

Overall, BRCA1 mutations were more common in Caucasian women (2.9 percent) versus African-American women (1.4 percent) and in Jewish (10.2 percent) vs. non-Jewish (2 percent) women.

Mutations in BRCA2 were slightly more common in African-American women (2.6 percent) than in Caucasian women (2.1 percent).

Research Focused on Prevalence in African-American Women

To date, most of the studies on BRCA1 and BRCA2 mutations have focused on families known to be at high risk for breast cancer and on women who develop breast cancer at a relatively young age.

The new study looked at the prevalence and predictors of BRCA1 and BRCA2 mutations in under-studied groups of women, such as African Americans and older women.

This is one of the first studies to look at the prevalence of BRCA1 and BRCA2 mutations in African-American women.

"The lack of research has led to the impression that it's more of a problem for Caucasian women," says lead investigator Kathleen E. Malone, Ph.D., of the Fred Hutchinson Cancer Research Center, in Seattle.

"Our study shows that the overall frequency of mutations is generally similar across these two races, and so, at the very least, clinicians and women who are African American should be thinking about this to the same extent as Caucasian women," she says.

The researchers also looked at factors which predicted whether a woman carried one of the mutations. The strongest predictors of carrying a BRCA1 mutation were being diagnosed with breast cancer before the age of 45 or having a relative diagnosed before the age of 45, or ovarian cancer in a relative, as well as having Jewish ancestry.

Early age at diagnosis in the patient or in relatives was a predictor of BRCA2 mutation status.

This information is critical for identifying which women might benefit from genetic testing.

"The study basically confirms that the No. 1 way to predict whether a person is going to have one of two genetic mutations is something really cheap: talk to the patient, ask them about their family history," says Dr. Jay Brooks, chairman of hematology/oncology at Ochsner Health System, in Baton Rouge, La.

"Early age of onset of breast cancer and family history of ovarian cancer are two of the strongest predictors," he adds.

Always consult your physician for more information.

 

 

  
 
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