PGx TAMOXIFEN

Scientifically reviewed | Last updated July 14, 2025
For more information see our editorial policy

CYP2D6

The active substance tamoxifen is a prodrug that is converted in the body into the active metabolite endoxifen. The polymorphic enzyme CYP2D6 plays a key role in this process. Clinical data suggest that polymorphisms in the CYP2D6 gene, which lead to reduced CYP2D6 activity, may impair the efficacy of tamoxifen therapy. This is particularly true for homozygosity of non-functional CYP2D6 alleles (poor metabolizer phenotype). In patients with no CYP2D6 activity, significantly lower levels of the active metabolite endoxifen have been detected.

 

Information on the relationship between CYP2D6 genotype and endoxifen levels has been included in the official prescribing information for tamoxifen, and dosing and treatment recommendations for tamoxifen in relation to the CYP2D6 genotype can be found in various tamoxifen and CYP2D6 guidelines. It has also long been known that the concurrent use of CYP2D6 inhibitors (e.g., paroxetine) with tamoxifen leads to reduced endoxifen levels due to drug interactions.

 

Determining the CYP2D6 metabolizer type serves to estimate the risk of tamoxifen resistance. Currently, testing the CYP2D6 gene is particularly considered for postmenopausal patients in whom tamoxifen is to be used as an alternative to therapy with aromatase inhibitors.  Measuring endoxifen levels prior to or alongside genotyping, may also be considered.

 

References

Fachinformation Tamoxifen / Goetz et al. 2018, Clin Pharmacol Ther 103:770 / Drögemöller et al. 2019, Breast Cancer Res Treat 173:521 / Swenn et al. 2011, Clin Pharmacol Ther 89:662

GENES
CYP2D6
HOW CAN YOU GET TESTED?
Step 1: Visit healthcare professional
Step 2: Sample collection (blood or buccal swab)
Step 3: Sequencing performed at our accredited laboratory
Step 4: Medical report
Step 5: Genetic counselling
FAQ

How does pharmacogenomic testing improve therapy with anticancer drugs?

Can I order tests to assess the toxicity risk of cancer therapies other than tamoxifen?

How long does it take to receive PGx Tamoxifen test results?

CONTACT US

Please get in touch with us for any questions, inquiries, feedback or with any comments you might have.

LATEST ARTICLES

The Human Genome Project, created to determine the sequence of the human genome, was one of the most important biomedical research projects of the 20...

Read more

The endometrial microbiome is increasingly recognized as a factor in reproductive health, and imbalances in microbial composition have been linked to...

Read more

Spinal muscular atrophy is a rare genetic condition that weakens muscles by affecting the motor nerve cells in the spinal cord. It is a leading genet...

Read more

Summer encourages people to spend more time outdoors, soaking in the sun and enjoying the season’s warm weather. While sunlight can have beneficial...

Read more

We're thrilled to share the results of Medicover Genetics essay competition for high school students as well as the two winning essays. This competit...

Read more

Cystic fibrosis (CF) is a life-threatening, progressive, inherited condition that causes severe damage to the body, primarily affecting the organs of...

Read more

Down syndrome is a genetic condition caused by the presence of an extra copy of chromosome 21. It affects physical growth, facial features, and cogni...

Read more

Every year on April 25th, DNA Day celebrates the discovery of DNA’s double helix and the advances we’ve made in understanding genetics. D...

Read more

Neurodevelopmental disorders (NDDs) have diverse genetic origins, making diagnosis challenging. A new study analyzing over 1,100 pediatric patients f...

Read more

Colorectal cancer (CRC) remains one of the most prevalent and deadly cancers worldwide, with a significant number of cases presenting at an advanced ...

Read more