What Testing for Tamoxifen Response Tells You

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 your 2D6 genes indicate that you are a "Poor Metabolizer," studies show that you may not receive the full medical benefit from taking tamoxifen.

FDA Recommends Relabeling Tamoxifen

On October 18, 2006 an FDA panel unanimously agreed that the 2D6 genes are a predictor of tamoxifen efficacy. They recommend relabeling tamoxifen to say that 2D6 poor metabolizers who take tamoxifen have a higher risk for breast cancer recurrence, and that testing is available.

The 2D6 gene is involved in the metabolism of many drugs, including some over-the-counter medications. Different people have different variations of this gene. Some variations metabolize 2D6 drugs very quickly, while others don't metabolize them as well. Still others don't metabolize them at all. Knowing your genetic status may be useful to you in the future, should you be prescribed or consider taking other medications that are processed by 2D6. See the table below for a list of drugs known to be metabolized by 2D6.

Talking With Your Doctor

Healthcare is a team effort. Knowing your 2D6 status is important information for you and your doctor. However, because genetic testing for drug response is a new and growing area, not all physicians are familiar with it or have it integrated into their practice.

If you are taking tamoxifen or other drugs processed by 2D6, your test results may help you and your doctor if you are experiencing:

• Unexpected or severe side effects
• No therapeutic response or lower-than-expected therapeutic response
• Elevated liver enzymes or toxicity

If you already know your 2D6 status, it is very important to talk with your doctor so that he or she can adjust your prescriptions accordingly.