Cytochrome P450 2D6 Testing for Tamoxifen Resistance

Tamoxifen is a medication for the treatment of breast cancer or for people at a high risk of developing breast cancer.

Recent research has shown that 7-10% of women with breast cancer may not receive the full medical benefit from taking tamoxifen due to their unique genetic make-up. These women have a version of a gene called Cytochrome P450 2D6, which reduces the effectiveness of tamoxifen and increase their chance of breast cancer recurrence.

Since more than 25% of all clinically used medications are metabolized by 2D6, knowing your 2D6 status can help you and your doctor with the future selection of medications.

Genetic testing can tell whether tamoxifen is likely to be an effective treatment for you. This test looks at a specific gene, called 2D6, to determine whether your body can fully metabolize tamoxifen to its active form, endoxifen. If tamoxifen is not an effective treatment, your physician may recommend aromatase inhibitors.

Who Should Be Tested

The CYP2D6 test for tamoxifen is considered appropriate for women who are taking or considering taking tamoxifen to prevent the recurrence of breast cancer. It is especially important if the patient is also taking or considering co-administration with SSRIs.