2D6 Test Results

Tamoxifen is a medication for the treatment of breast cancer or for people at a high risk of developing breast cancer. I am currently taking 20mg of Tamoxifen on a daily basis. My course of treatment, is to be on this drug for the next 5 years. I'm 6 months into it.

I think I have been doing very well. The first several weeks I experienced intermittant nausea and hot flashes. Those, soon subsided. My menstrual cycles have been normal up until last month. It never came. This might be the start of no more periods or irregular menstrual periods.

The reason why I requested the test is because 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. This percentage may have a version of a gene called Cytochrome P450 2D6, which reduces the effectiveness of tamoxifen and increase their chance of breast cancer recurrence.

Genetic testing can tell whether tamoxifen is likely to be an effective treatment for me. This test looks at a specific gene, called 2D6, to determine whether ones body can fully metabolize tamoxifen to its active form, endoxifen.

My doctor called me today to tell me that I am an extensive metabolizer. She also added that this is the reason why I'm tolerating the drug so well. I'm happy with the results. Knowing that I'm taking a drug that can benefit me gives me peace of mind.

How to interpret the results if you have been tested (studies were done in post menopausal women with tamoxifen dose 20mg daily but biologically likely to also apply to pre-menopausal women)

Ultra rapid metabolizer: You rapidly convert tamoxifen to endoxifen. You get maximal benefit.

Extensive metabolizer: You normally convert tamoxifen to endoxifen. You get usual benefit.

Intermediate metabolizer: You have half the capacity to convert tamoxifen to endoxifen. You may or may not get usual benefit.

Poor metabolizer: You have limited capacity to convert tamoxifen to endoxifen. Your concentration of endoxifen is only 25% of that in tamoxifen treated extensive metabolizers. In some studies in postmenopausal women ER+ on tamoxifen 20 mg/d for 5 yrs after diagnosis, poor metabolizers have 70-80% less disease free survival than non-poor metabolizers.