deCODE BreastCancer™
The deCODE BreastCancer™ test is a novel, DNA-based reference laboratory test for the first common genetic risk factors to be identified that contribute to a substantial proportion of female breast cancers in the general population.
The deCODE BreastCancer™ test determines whether the subject has inherited the risk or non-risk version at 7 different variable sites in the human genome. By comparing deCODE BreastCancer™ test results to the general risk of women in the population it can be seen whether the person tested has a risk greater or lower than the average population risk. The risks at each of the 7 markers are multiplied together to define combined risks from 0.4-to 4.0- fold the relative general population risk. The deCODE BreastCancer™ test examines only genetic risk factors, so other factors such as age and hormonal factors need also to be taken into account. By combining the test results and risks associated with other known risk factors, a more complete lifetime risk estimate can be generated.
The test is done on the DNA isolated from an inner cheek or a blood sample, and it looks at 7 marker variants (SNPs, single nucleotide polymorphisms) in the genome that people inherit from their parents and have been associated with increased risk for breast cancer. These variations are very common in the population but have been shown to affect a woman’s risk of getting breast cancer. The validity of these 7 variants as risk factors for the common forms of breast cancer has been demonstrated in large, multinational discovery and replication studies involving nearly 100,000 breast cancer patients and healthy control subjects.
According to the test results, only about 5% of women have an average 2-fold risk for breast cancer compared to the general population, and about 1% have a 3-fold risk. This translates for white women to a lifetime risk of 24% and 36%, respectively, versus the average population-based risk of 12%. It is estimated that these 7 markers together account for 60% of breast cancer (population attributable risk).
Breast cancers can be classified as either estrogen receptor positive (ER+) or estrogen receptor negative (ER-), depending on whether they contain certain proteins that allow the cancer to respond to the female sex hormone estrogen, which can make the breast tissues more susceptible to hormonal risk factors and drive small tumors into larger tumors. Several of the genetic variants examined by the deCODE BreastCancer™ test affect the chance that a breast tumor, if it arises, will be ER+ or ER-. At the same time, ER+ tumors may be more amenable to prevention by drugs that target the estrogen pathway, such as tamoxifen.
The deCODE BreastCancer™ test does not test for what is generally referred to as familial or inherited forms of breast cancer caused by rare mutations in breast cancer genes such as BRCA1, BRCA2, TP53, and PTEN. These mutations confer extremely high risks of breast cancer and occur only in rare families that may have exceptionally high numbers of breast cancer cases, often arising in younger women and sometimes along with ovarian cancer. Mutations in these genes need to be tested for separately under the guidance of a genetic counselor. However, for individuals who are known to carry mutations in these genes, the deCODE BreastCancer™ test provides additional information on their overall risk of breast cancer since some of the test markers are shown to influence the effect of these rare breast cancer gene mutations.
The deCODE BreastCancer™ test is performed in deCODE’s CLIA-registered laboratory. The test can only be ordered by qualified physicians and medical practitioners. If you are an individual interested in deCODE BreastCancer™, you can continue reviewing this site, and even download and print the test order forms to meet with your doctor and discuss the next steps.
The test is currently only valid for women of white European origin since it’s validation in other ethnic groups has still not taken place.