How Testing for Tamoxifen Response Works
Genetic testing for tamoxifen response looks for common variants in the CYP2D6 gene using cells taken from swabbing the inside of your cheek or from a blood sample. Our genes are the instruction manuals for making the enzymes we need to process food, drugs, and other chemicals that enter our body.
We all have genes that don’t work in the usual way. This happens because we inherit small variations in our instructions that make us unique.
The CYP2D6 gene tells the body how to make an enzyme that metabolizes, or changes, tamoxifen and other drugs. The “normal” forms of the CYP2D6 gene are called *1 and *2. Other common variants in the CYP2D6 gene — called *3, *4, *5 and so on — lower the body's ability to metabolize tamoxifen to its active forms.
People have two copies of the CYP2D6 gene – one from each parent. This test tells you what combination of CYP2D6 genes you have. Testing for CYP2D6 variants is reliable and accurate.
Testing for genetic variants in CYP2D6 can't find all of the variants that change how the CYP2D6 enzyme works. Most laboratories look for 10 or more common variants, which account for most cases of poor tamoxifen response in most ethnic groups.
A normal test result can't predict exactly how well tamoxifen will work for you. Many factors can change how we respond to drugs.
