According to the National Cancer Institute, each year mutations in the BRCA1 and BRCA2 genes are linked to over 20,000 cases of breast cancer in the United States. Known mutations in these two genes increase the likelihood by five-fold that an individual will eventually develop cancer. Those interested in testing should consult with their doctor or genetic counselor, who will outline the patient's available testing options and possible results, help determine which would be most appropriate, put their patient in contact with a testing agency or research group, and eventually help understand the results. A blood sample would be sent for genetic testing to determine whether an individual has cancer-associated mutations in either gene. In the U.S., the company Myriad Genetics and Laboratory has held a patent for commercial testing, although this patent was struck down in late March 2010.
Common Clinical and Research Testing
International clinics and researchers can perform several tests on the BRCA1 and BRCA2 genes. One approach is for researchers to read the entire DNA sequence for each gene, looking for differences from the normal sequence. They can also read the DNA sequence of areas known to frequently have mutations. Other tests involve scanning for regions that do not physically match the normal copy, then reading the DNA sequence of nonidentical regions. Researchers can look for specific known mutations or for DNA loss or duplication. While becoming involved in a research project may provide free testing, often the project requires that multiple family members participate and/or that the results remain anonymous or incomplete.
Myriad Comprehensive Analysis
The comprehensive Myriad test looks for any variations from the normal for both genes. This type of test would be recommended for an individual where there is a familial pattern of breast cancer but there have been no mutations to BRCA1 or BRCA2 identified. The test involves determining the exact DNA sequence of the coding parts of BRCA1 and BRCA2, that is, the regions of the genes responsible for making the BRCA1 and BRCA2 products.
Myriad Single Site Analysis
If a mutation has previously been found to be linked to an increased incidence of breast cancer in a particular family, then single site analysis can be used. This test will show whether or not an individual has the specific mutation known to run in this family.
Myriad Multisite Three Analysis
Many populations, as for example the Ashkenazi Jewish population, were established by a relatively small group of people, and so their genetic variation is relatively decreased. Inherited mutations in BRCA1 and BRCA2 in some Eastern Europeans are usually the same three mutations. Individuals with this background can choose to have multisite three analysis done to rule out the most likely mutations for their heritage.
Myriad Results
The Myriad tests can yield three results: positive, negative or ambiguous. It is recommended that an individual consult with a genetic counselor or doctor to understand the significance of the results. A positive or negative result indicates that an individual has an increased or decreased risk of developing cancer, respectively, not that they are guaranteed to either develop or avoid breast cancer. An ambiguous result occurs when a different DNA sequence than the normal sequence is found but the mutation present has not been linked to an increased probability of breast cancer. As well, Myriad automatically updates results, especially those that were ambiguous, as new information is obtained.
References
- National Cancer Institute: BRCA1 and BRCA2: Cancer Risk and Genetic Testing
- SFGate: US Judge Strikes Down Patent on Cancer Genes
- National Center for Biotechnology Information GeneTests: BRCA1 Hereditary Breast/Ovarian Cancer
- National Center for Biotechnology Information GeneTests: BRCA2 Hereditary Breast/Ovarian Cancer
- Myriad Genetics and Laboratory: Understanding my BRACAnalysis Test Results
