The Role of Genes in Increasing Risk for Breast Cancer
Some women carry certain genetic changes in their BRCA genes, which stands for BReast CAncer susceptibility gene, that increase their risks for getting breast, ovarian, and other kinds of cancers at a young age. To better understand how the BRCA genes affect breast cancer risk, we first need to understand more about genes.
What are genes?
Genes carry the information that determines which features or characteristics are passed on to you — or inherited — from your parents. The Human Genome Project has estimated that humans have between 20,000 and 25,000 genes.
Every person has two copies of each gene, one from each parent. Most genes are the same in all people, but a small number of genes (less than 1 percent of the total) are slightly different between people. These small differences contribute to each person’s unique physical features.
What are the BRCA genes?
The BRCA genes are responsible for giving the body instructions to overcome tumors. There are two BRCA genes: BRCA1 and BRCA2. Normally, they help protect you from getting cancer. But when you have changes or mutations on one or both of your BRCA genes, cells are more likely to divide and change rapidly, which can lead to cancer.
The BRCA1 gene is involved in fixing damaged DNA (deoxyribonucleic acid) which carries genetic information. By helping to repair DNA, the BRCA1 gene plays an important part in keeping genetic information safe.
Breast and ovarian cancer are the most common diseases linked to BRCA1 and BRCA2 mutations, but mutated forms of the BRCA genes may increase people’s risk for other cancers as well. These mutations are present in every cell in the body and can be passed from one generation to the next. As a result, they are associated with cancers that gather in families. Not everyone who inherits a mutation in the BRCA1 gene will develop cancer. Other genetic, environmental, and lifestyle factors also contribute to a person's cancer risk.
For example, men with BRCA2 mutations are at increased risk of getting prostate cancer.
Women with BRCA1 gene mutations have a 55 to 65 percent chance of developing breast cancer by age 70. Women with BRCA2 gene mutations have about a 45 percent chance of developing breast cancer by age 70.
Women with BRCA1 gene mutations have a 35 to 60 percent chance of developing ovarian cancer in their lifetimes, as compared with 1.6 percent in the general population.
At least five inherited BRCA1 gene mutations have been found to increase the risk of prostate cancer. Men who carry a BRCA1 gene mutation that increases the risk of prostate cancer may also be at increased risk for other cancers.
Inherited mutations in the BRCA1 gene also increase the risk of several other types of cancer, including pancreatic cancer and colon cancer. It is not clear why different individuals with BRCA1 mutations develop cancers in different organs. There could be other factors related to environment and lifestyle choices that may contribute to cancer in different organs.
What is genetic testing?
Genetic testing to look at your genes and may be used to see if you have a higher risk of health problems. They can also be used to help choose treatments and see how the treatments are working.
What can I learn from testing?
There are many different types of genetic tests. Genetic tests can help to:
• Diagnose disease
• Identify gene changes that are responsible for an already diagnosed disease
• Determine the severity of a disease
• Guide doctors in deciding on the best medicine or treatment to use for certain individuals
• Identify gene changes that may increase the risk to develop a disease
• Identify gene changes that could be passed on to children
• Screen newborn babies for certain treatable conditions
Genetic test results can be hard to understand, however specialists like geneticists and genetic counselors can help explain what results might mean to you and your family. Because genetic testing tells you information about your DNA, which is shared with other family members, sometimes a genetic test result may have implications for blood relatives of the person who had testing.
Who Should Consider Genetic Testing?
There are many reasons that people might get genetic testing. Doctors might suggest a genetic test if patients or their families have certain patterns of disease. Harmful BRCA1 and BRCA2 gene mutations are not very common. Most experts agree that testing is not necessary for everyone. Only people who have individual or family history of a harmful mutation in BRCA1 or BRCA2 should be tested.
A geneticist or genetic counselor can help families think about the benefits and limitations of a particular genetic test.
U.S. National Library of Medicine (2016). Genetics Home Reference. Bethesda, MD: National Institutes of Health https://ghr.nlm.nih.gov/