Inherited Breast Cancer
About 80% of women who develop breast cancer have no identifiable risk factors for breast cancer other than age. The remaining 20% of women may have one or more blood relatives with breast cancer, and of those women, less than half will have cancer as a result of a clearly identifiable inherited genetic factor. Overall, about 5-10% of women who develop breast cancer have a clearly identifiable inherited genetic factor.
In this NetWellness feature you will find information on the following:
- Heredity Cancer Susceptibility Syndromes
- Genes: What They Are and How They Work
- Heredity Cancer Susceptibility Genes
- Risk Factors
- Genetic Counseling
- Testing for Genetic Mutations
- Screening for All Women
Heredity Cancer Susceptibility Syndromes
These families have what is referred to as a hereditary cancer susceptibility syndrome. In families with hereditary cancer susceptibility syndromes, cancers occur:
- At earlier ages
- In multiple generations
- In multiple members in each generation
Hereditary cancer susceptibility is caused by inherited genetic changes, or mutations, in specific genes.
Genes: What They Are and How They Work
About Our Genes
- The instructions that direct the working and growth of the cells in our bodies
- Contained on the chromosomes
- Inherited – half of our genes from our father and half of our genes from our mother in the sperm and the egg, respectively, that united to form us.
- Responsible for traits that are inherited, such as eye color, hair color or blood type.
Normal variations in genes create the variability that makes each of us unique.
The most important genes with respect to the development of cancer are the tumor suppressor genes. Tumor suppressor genes usually make sure that cells stop growing at specific times so the number and type of cell is appropriate. If a tumor suppressor gene is damaged, it may prevent that gene from maintaining regular, controlled cellular growth and division.
How Tumors Develop
A tumor develops when several tumor suppressor genes are damaged and cells are allowed to divide without being controlled. Cancers are tumors that invade normal tissue.
Most genes are present in two copies in each cell. If one copy of a pair of genes is damaged, the remaining copy is usually able to carry on the normal function. However, if the second copy of a tumor suppressor gene is damaged, the cell is now without a working copy to regulate cell growth.
In some ways, it is like having front and rear brakes on a bicycle. If either the front or rear brake is damaged, there is another brake to help stop. However, if both brakes are damaged, the bicycle cannot be controlled properly.
Inheriting a Mutated Gene
Because we are born with two copies of all our genes, it is possible to be born with one copy of a tumor suppressor gene that is not working, and yet develop quite normally. However, if the second copy is damaged, a cell may proceed through a number of additional steps involving more genetic mistakes to become a cancer. The damage to the second copy can be the result of the normal inaccuracy of cell division or by exposure to carcinogens.
Why Cancer Develops Earlier if You Have a Mutated Gene
When someone inherits a mistake, or mutation in a tumor suppressor gene, it is like starting out one step into the process of cancer development. This is why cancers generally occur at younger ages in families with hereditary cancer susceptibility.
Your Chances of Inheriting a Mutated Gene
If someone is born with a mutation in a cancer susceptibility gene, their children will usually have a 50/50 chance of inheriting this mutation from that parent, and a 50/50 chance of inheriting their normal copy. Children who inherit the copy with the mutation are at increased risk to develop cancer, while those who inherit the normal copy are not at an increased risk – in other words they are just as likely as another average person to develop cancer.
Hereditary Cancer Susceptibility Genes
“Hereditary cancer susceptibility genes” are genes that have been found to cause a genetic tendency to develop breast cancer and ovarian cancer when there are inherited mutations in these genes. The most common genes found to increase the risk of breast and ovarian cancer are:
- BRCA1 (Breast Cancer1)
- BRCA2 (Breast Cancer2)
Individuals with BRCA1 mutations are at increased risk for breast and ovarian cancers. It is reported that women who carry alterations in the BRCA1 gene have up to an 85% lifetime risk of developing breast cancer and a 40-60% lifetime risk of developing ovarian cancer. This is compared to the 10-12% lifetime risk of breast cancer and 1-2% lifetime risk of ovarian cancer for the average woman.
Males who carry alterations in BRCA1 may be at somewhat increased risk for breast cancer, and are at increased risk for prostate cancer.
Mutations in BRCA2 account for up to 15% of families with hereditary breast cancer. Women who carry alterations in BRCA2 have up to an 85% lifetime risk of developing breast cancer and up to 27% risk of developing ovarian cancer.
Males who carry alterations in BRCA2 are estimated to have a 5-10% risk of breast cancer.
Having a family history of breast cancer is an important risk factor for the disease, especially if a mother or sister (first degree relative) has had breast cancer before entering menopause. Women who have one first-degree relative with breast cancer run a risk of 1.5-2 times the usual risk of developing the disease. The risk can be 4-6 times higher if the woman has two first degree relatives with breast cancer.
Studies indicate that the hormone of primary concern is estrogen. While it is not advisable to eliminate estrogen exposure completely, it is also not advisable to increase unnecessary exposure. Women have a higher chance of developing breast cancer if:
- Begin their menstrual periods before the age of 12
- Enter menopause late
- Do not have children
- Use hormone replacement therapy for an extended length of time after menopause.
Genetic counseling is available to individuals and families with a medical history or increased personal risk for a wide range of genetic conditions. Genetic counseling provides patient with:
Medical geneticists and genetic counselors are health professionals with specialized training and experience in human and medical genetics and counseling who can give information and supportive counseling concerning many disorders or abnormalities. Genetic specialists should have certification from the American Board of Genetic Counseling or the American Board of Medical Genetics.
Some examples of how the services offered by genetic counselors include:
- Education about causes and risk factors associated with a number of birth defects and hereditary conditions
- Advise patients of the tests available that may provide information about the potential to develop hereditary conditions, or the chance of having children with genetic or hereditary disorders.
- Work with individuals to understand the implications of hereditary conditions for themselves and their families.
- Discuss options for early detection, risk reduction and predictive testing.
To find a genetic counselor in your area, please see the National Society of Genetic Counselors Resource Center website (www.nsgc.org).
Testing for Genetic Mutations
Women considering genetic testing for hereditary breast cancer susceptibility must receive genetic counseling for accurate and unbiased information about the benefits, risks and limitations of testing.
Potential Harm from Genetic Testing
Women must weigh the benefits of genetic testing against the potential harms that might result from genetic testing. These include the significance of this information for:
- Their families
- Whether more intensive screening or risk reducing options will be acceptable to them
Some important facts to consider about being tested for BRCA1 and BRCA2 mutations are:
- The test does not prevent cancer in women who carry the mutation.
- It cannot cure or detect existing disease.
- Having a genetic susceptibility to breast or ovarian cancer does not mean that a woman will inevitably develop cancer, only that her chance of developing cancer is substantially higher than the risk for women who do not have inherited cancer susceptibility mutations.
- Not all results can be interpreted as normal or harmful.
- Not all genes that contribute to increased risk for breast cancer have been identified.
- If a woman tests negative for the gene mutation, it does not mean she will not develop breast cancer. Every woman still has at least the population risk to develop breast cancer.
- The test is expensive.
Discrimination Due to Genetic Testing – It’s Not a Problem Yet
Many people are concerned that they will experience insurance or employment discrimination if they are found to have genetic testing. To date, there have been no proven instances of people losing health insurance or being denied employment because of a positive genetic test for hereditary breast cancer.
Protection Under the Law
There is some federal legislation that is thought to provide some protection against health insurance discrimination and employment discrimination. In May of 2008 the president signed the Genetic Information Non-discrimination Act (GINA) into law. The first portion of the bill went into effect in May of 2009, and the second portion of the bill went into effect in November of 2009.
GINA was designed to prevent health insurance and employment discrimination on the basis of a genetic testing result. The bill prohibits the use of a genetic testing result as a “pre-existing condition.” This protection does not extend to life, disability or long-term care insurance.
A number of states also have specific legislation prohibiting health insurance discrimination or employment discrimination on the basis of genetic testing information. Additional information about laws protecting individuals from genetic discrimination can be found at the following websites:
Benefits of Genetic Testing
Genetic testing can be useful in identifying women who are at particularly high risk of developing breast or ovarian cancer. Knowing this information gives a woman:
- The opportunity to make choices that have the potential to decrease her risk of developing cancer
- Ensure that she is having close screening to detect cancers early
- The opportunity to alert other family members to possible increased risk
Screening for All Women
Women with a strong family history of breast cancer, whether or not they are found to have mutations in genes associated with hereditary breast cancer susceptibility, should be using regular breast cancer screening. This should include:
- Yearly mammograms
- Clinical breast exams every 6-12 months
- Monthly breast self-exams
The earlier cancer is detected, the greater the chance for a cure.
Additional information is available about breast cancer risk and screening on the website for the National Cancer Institute.
More information about Cancer Genetics:
- Genes, Chromosomes and Cancer Genes
- Cancer Genetic Counseling – Getting the Information You Need
- Inherited Cancers
- Inherited Breast Cancer
- Back to the Cancer Genetics Overview
For more information:
Go to the Breast Cancer health topic.