Tamoxifen

Adverse Drug Reaction Testing for Tamoxifen (Nolvadex)

Is your physician thinking of prescribing Tamoxifen?

Are you currently taking Tamoxifen?

Are you concerned about drug safety?

If you answered yes to any of these questions, consider ordering Prescription Drug Reaction Testing.

Genelex will be happy to mail information to you or to your healthcare provider on your behalf, simply complete the request form.

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. The evidence is so strong that an FDA panel recently recommended that the label of tamoxifen be changed to say that 2D6 poor metabolizers who take tamoxifen have a higher risk for breast cancer recurrence, and that testing is available.

DNA Drug Reaction Testing can examine your DNA variations in 2D6 and other important drug processing pathways. Your physician can use this information to adjust dosage and select medications that will be the safest and most effective for you. Since more than 20% 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. Order DNA drug reaction testing directly by calling Genelex at (800) 523-3080 or ordering online.

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.

The Research

Tamoxifen is a prodrug widely used to treat, and as prophylaxis for estrogen receptor positive breast cancer. Out of the approximately 120,000 new ER positive breast cancer patients per year: 41,000 of whom will die, 42,000 are predicted to fail tamoxifen treatment because of 2D6 poor metabolizer phenotype (Jemail 2006). "Hot flashes," a common side affect, is typically treated with SSRIs, many of which are potent inhibitors of CYP2D6, phenol-converting intermediate metabolizer patients into 2D6 poor metabolizers, now demonstrated as crucial to the activation of tamoxifen to endoxifen. Endoxifen has a 100X greater receptor affinity than tamoxifen and is 30-100 times more effective (FDA 2006).

CYP2D6 genetically normal metabolizers also taking an inhibitor had 58% lower endoxifen levels and are likely to be in the group of about 35% of patients who don't respond to tamoxifen. CYP2D6 frank poor metabolizers, homozygous for *3,*4, *5, and *6, had endoxifen levels 26% of WT. CYP2D6*4/*4 PMs had a 3.12 hazard ratio for breast cancer relapse. Two year relapse free survival is 68% in patients with the 2D6 PM phenotype and 98% in Extensive Metabolizers(Goetz 2005, 2007). This suggests that widespread genotyping and therapeutic drug monitoring could result in successful outcomes for many of the 35% of ER positive breast cancer patients who currently fail tamoxifen treatment.

The Testing Process

The process is simple. We send you prepaid return mailing supplies and a cheek swab collection kit. You collect your samples in the privacy of your home and return them in the packaging provided. Results are typically available two weeks from the receipt of samples in our lab. Four-day (STAT) testing is available for an additional fee.

Ordering Tests

Call Genelex today at (800) 523-3080, order on-line, or download the order form and fax or mail in your order. Don't forget to take a look at our other informational genetic testing products now as you receive significant discounts when ordering tests at the same time.

If you were referred by the National Foundation for Cancer Research, please let us know, and a portion of the testing proceeds will be donated to NFCR.

Note: Testing is currently not available to New York residents and can only be ordered through a physician in Maryland and California.