Your DNA
The genetics of breast cancer
Most of the risk of breast cancer comes from a combination of lifestyle and environmental factors, but studies of twins show that about 27 percent of the risk for breast cancer is genetic. A good part of this inherited risk appears to result from combinations of common genes, each with a modest effect. This means that many people have these genes, but the increased risk associated with each gene is relatively small.
Knowing your inherited risk factors can help guide your lifestyle habits. Depending on your genetic makeup, you may respond better or worse than others to certain drugs and treatments. As knowledge about genetic risk factors advances, it can illuminate ways to tailor more effective prevention and treatment strategies.
You've probably heard about BRCA, the first gene linked to breast and ovarian cancer. Navigenics does not test for the BRCA variants, which account for less than 10 percent of all breast cancer cases. People with a family history of breast cancer, especially in a close relative such as a parent or sibling, should consider consulting a genetic counselor.
At Navigenics, we focus on the 90 percent of breast cancer cases that are not caused by such rare variants. We look for genetic markers that are common in the U.S. population.
What we found for breast cancer
We looked at seven places on your genome where a one-letter difference in the genetic code raises your odds of breast cancer. At each location, there are two markers, for a total of 14 possible risk markers. You have 10 of the 14 risk markers we looked for.
Breast cancer
- You:
- 20%
- Avg:
- 13%
Your genetic markers
|
Gene or location 
|
Risk marker
|
Your markers
|
Odds ratio
|
Source
|
|---|---|---|---|---|
|
TNRC9
|
A | G G | 1.0 | Nature Genetics, 2007 |
|
FGFR2
|
A | A A | 1.63 | Nature, 2007 |
|
chr2.217614077
|
A | A A | 1.44 | Nature Genetics, 2007 |
|
CASP8
|
G | G G | 1.35 | Nature Genetics, 2007 |
|
MAP3K1
|
C | A C | 1.13 | Nature, 2007 |
|
chr8.128424800
|
G | G G | 1.18 | Nature, 2007 |
|
LSP1
|
C | C T | 1.06 | Nature, 2007 |
What it means
Everyone has some chance of developing breast cancer. Each risk marker increases your odds by a different amount — some a little, some a lot. The "odds ratio" column in the chart above shows their relative impact.
About genetic markers
More than 99 percent of our genetic code is identical from person to person. The remainder is unique among individuals and gives rise to our diversity. DNA, the chemical instructions that determine our genetic code, is inherited from our parents and is composed of four biochemical bases that are represented by the DNA alphabet: A, T, G and C.
SNPs, or single nucleotide polymorphisms, are one-letter variations in our DNA. Each SNP (pronounced "snip") consists of two markers or variants, one inherited from each of our parents, and each marker has two possible versions, a risk version and a non-risk version. For example, at a given SNP, the base A may be the risk marker and the base G may be the non-risk marker. At another SNP, G may be the risk marker and T the non-risk marker.
The SNPs included in your Navigenics risk estimate have been reliably shown to be associated with diseases, although it is not known exactly how they contribute to the conditions. The degree of genetic risk you inherit is related, in part, to how many risk markers you have residing at each SNP — none, one (from one parent) or two (one from each parent). Just because you may have one or even two risk markers does not mean that you will definitely develop a given health condition, but it can raise your risk, especially if other lifestyle or environmental risk factors are present.