DNA Test Helps Tailor Breast Cancer Treatment

In 2007, nearly 180,000 women were diagnosed with breast cancer, and 40,000 died from it. Two-thirds of these breast cancers required estrogen, the naturally occurring female sex hormone, to grow and spread—these are known as ER+ (estrogen receptor positive) cancers. Tamoxifen, a drug that works by blocking the effects of estrogen in breast tissue, theoretically can be very effective in treating these cancers and preventing their recurrence.

Unfortunately, 35% of ER+ breast cancer patients do not respond to tamoxifen treatment. However, recent advances in research may make it possible to reduce the failure rate of tamoxifen treatment to less than 10% by using a simple DNA test and carefully managing other medicines a patient is taking. This could greatly improve treatment outcomes for many of the 500,000 women currently taking tamoxifen.

Before tamoxifen can be effective it has to be metabolized and converted to endoxifen, which is 30 to 100 times more potent than tamoxifen itself. The conversion of tamoxifen to endoxifen is carried out in the liver by an enzyme called CYP2D6. We now know that some women do not have the CYP2D6 enzyme because of inherited changes to their DNA. These patients do not respond well to tamoxifen, and are twice as likely to see their breast cancer return.

Another reason that causes tamoxifen failure for many patients is the lack of ability to convert tamoxifen to endoxifen because of other medicines they are taking. “Hot flashes,” for example, are a common side effect of tamoxifen and are often treated with antidepressants. Researchers have found that these and many other medicines reduce the ability of the CYP2D6 enzyme to complete the conversion of tamoxifen to endoxifen. Women with already lowered levels of CYP2D6 (caused by inherited changes and other reasons) are most affected.

Now, a simple DNA test available from Genelex (a licensed medical laboratory) can determine a woman’s ability to produce CYP2D6. Included with the test is a software program, GeneMedRx, which interprets the DNA test results within the framework of all of the medicines the patient is taking. This vital information helps oncologists identify patients with ER+ Breast Cancer for whom tamoxifen will work, and gives doctors a tool to make better treatment choices for each and everyone of their breast cancer patients.

For more information about the Genelex CYP2D6 DNA test, visit click HERE.