<h5 class="wp-block-heading" id="h-fda-now-recommends-genetic-testing-before-prescribing-specific-chemotherapy-medications">FDA Now Recommends Genetic Testing Before Prescribing Specific Chemotherapy Medications</h5>



For years, patient advocates have been calling for stronger safeguards against preventable toxicity from chemotherapy. Last week, the FDA took a major step forward, updating the label for a drug called <a href="https://medlineplus.gov/druginfo/meds/a699003.html" target="_blank" rel="noreferrer noopener">capecitabine</a> to explicitly recommend testing for variants in the DPYD gene before starting treatment. This is more than just a label change—it&#8217;s a long-awaited acknowledgment that genetics matter when it comes to patient safety.



<h2 class="wp-block-heading">What is DPYD?</h2>



The <a href="https://medlineplus.gov/genetics/gene/dpyd/" target="_blank" rel="noreferrer noopener">DPYD gene</a> provides instructions for making an enzyme called DPD (dihydropyrimidine dehydrogenase), which helps the body break down certain chemotherapy drugs like capecitabine and <a href="https://medlineplus.gov/druginfo/meds/a682708.html" target="_blank" rel="noreferrer noopener">5-fluorouracil</a>. These medications are commonly used to treat breast, colorectal, and other cancers. People with certain changes in this gene may not process these drugs properly, causing the drugs to build up in the body and, in some cases, leading to severe or even life-threatening <a href="https://medlineplus.gov/genetics/condition/dihydropyrimidine-dehydrogenase-deficiency/" target="_blank" rel="noreferrer noopener">reactions</a>.



<figure class="wp-block-image alignleft size-full is-resized"><img loading="lazy" decoding="async" width="508" height="531" src="http://35.88.189.111/wp-content/uploads/2025/10/drug-bottle.png" alt="" class="wp-image-34304" style="width:126px;height:auto" srcset="https://blog.pub.us-west-2.prd.23andme.us/wp-content/uploads/2025/10/drug-bottle.png 508w, https://blog.pub.us-west-2.prd.23andme.us/wp-content/uploads/2025/10/drug-bottle-287x300.png 287w" sizes="auto, (max-width: 508px) 100vw, 508px" /></figure>



These reactions can include painful mouth sores, severe diarrhea, low white blood cell counts, and nerve problems. <a href="https://medlineplus.gov/genetics/condition/dihydropyrimidine-dehydrogenase-deficiency/#frequency" target="_blank" rel="noreferrer noopener">Up to 8%</a> of people have a variant in the DPYD gene that affects how well they process these medications. Sadly, some patients with DPYD variants have died after receiving these drugs. Such experiences have fueled years of advocacy calling for genetic testing before treatment, not after. 



<h2 class="wp-block-heading" id="h-a-change-in-the-recommendations">A change in the recommendations</h2>



Until now, the FDA advised doctors they could &#8220;consider testing&#8221; patients before giving capecitabine or similar drugs. The <a href="https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/020896s052lbl.pdf" target="_blank" rel="noreferrer noopener">new label</a> goes much further, adding a warning that says, &#8220;serious adverse reactions or death may occur in patients with complete DPD deficiency&#8221; and telling doctors to test for DPYD variants before prescribing the medication. (Experts predict a similar change to the 5-fluorouracil drug label soon.) It&#8217;s a major win for patient safety and for the <a href="https://test4dpd.org/" target="_blank" rel="noreferrer noopener">advocacy groups</a> who have pushed tirelessly for this change. Organizations that have long advocated for universal DPYD testing hope this update will encourage hospitals and cancer centers across the U.S. to make pretreatment genetic testing standard care.



<figure class="wp-block-image alignright size-large is-resized"><img loading="lazy" decoding="async" width="790" height="1024" src="http://35.88.189.111/wp-content/uploads/2020/09/PGt-Home-790x1024.png" alt="23andMe mobile pharmacogenomics" class="wp-image-28527" style="width:256px;height:auto" srcset="https://blog.pub.us-west-2.prd.23andme.us/wp-content/uploads/2020/09/PGt-Home-790x1024.png 790w, https://blog.pub.us-west-2.prd.23andme.us/wp-content/uploads/2020/09/PGt-Home-231x300.png 231w, https://blog.pub.us-west-2.prd.23andme.us/wp-content/uploads/2020/09/PGt-Home-768x996.png 768w, https://blog.pub.us-west-2.prd.23andme.us/wp-content/uploads/2020/09/PGt-Home-679x880.png 679w, https://blog.pub.us-west-2.prd.23andme.us/wp-content/uploads/2020/09/PGt-Home-910x1180.png 910w, https://blog.pub.us-west-2.prd.23andme.us/wp-content/uploads/2020/09/PGt-Home.png 1583w" sizes="auto, (max-width: 790px) 100vw, 790px" /></figure>



We share the belief that genetic insights can empower individuals and help improve outcomes. The 23andMe® <a href="https://www.23andme.com/topics/pharmacogenetics/dpyd/" target="_blank" rel="noreferrer noopener">DPYD Drug Metabolism Pharmacogenetics report</a>*, available to <a href="https://www.23andme.com/membership/" target="_blank" rel="noreferrer noopener">23andMe+ Premium</a>™ members, provides information about two variants associated with reduced DPD enzyme activity. While this report isn&#8217;t a substitute for clinical testing, it can help people learn whether they carry certain DPYD variants and start a conversation with their healthcare provider. 



The FDA&#8217;s new label is an important step toward safer, more personalized cancer treatment and a long-awaited victory for the patients and advocates who made their voices heard.



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 * 23andMe PGS Pharmacogenetics reports: The 23andMe test uses qualitative genotyping to detect 3 variants in the CYP2C19 gene, 2 variants in the DPYD gene and 1 variant in the SLCO1B1 gene in the genomic DNA of adults from saliva for the purpose of reporting and interpreting information about the processing of certain therapeutics to inform discussions with a healthcare professional. It does not describe if a person will or will not respond to a particular therapeutic. Our CYP2C19 Pharmacogenetics report provides certain information about variants associated with metabolism of some therapeutics and provides interpretive drug information regarding the potential effect of citalopram and clopidogrel therapy. Our SLCO1B1 Pharmacogenetics report provides certain information about variants associated with the processing of some therapeutics and provides interpretive drug information regarding the potential effect of simvastatin therapy. Our DPYD Pharmacogenetics report does not describe the association between detected variants and any specific therapeutic. Results for DPYD and certain CYP2C19 results should be confirmed by an independent genetic test prescribed by your own healthcare provider before taking any medical action. Warning: Test information should not be used to start, stop, or change any course of treatment and does not test for all possible variants that may affect metabolism or protein function. The PGS test is not a substitute for visits to a healthcare professional. Making changes to your current regimen can lead to harmful side effects or reduced intended benefits of your medication, therefore consult with your healthcare professional before taking any medical action. For important information and limitations regarding Pharmacogenetic reports, visit <a href="http://23andme.com/test-info/pharmacogenetics/" target="_blank" rel="noreferrer noopener">23andme.com/test-info/pharmacogenetics/</a>

A Big Step Forward for Patient Safety

This interview is part of an occasional series of profiles introducing you to the people behind 23andMe’s compelling research. Chao Tian is a statistical geneticist, who came to 23andMe after <img loading="lazy" decoding="async" class="alignright size-medium wp-image-20935" src="https://blog-api.23andme.com/wp-content/uploads/2014/05/Chaos-Photo-200x300.jpg" alt="Chao's Photo" width="200" height="300" />studying Genetics and Statistics at UC Davis and working for two other genetics startups in the Bay Area. At 23andMe, Chao studies the genetic factors that affect drug response, and she is also working on improving our genome-wide association studies.
“Genetics is important, and we need more data to make it useful.”
<h6>Why are you excited about genetics? 
</h6>
I’ve always thought genetics was a very interesting field, especially after the human genome sequence was completed. Being able to decode yourself is very cool, and if you can understand yourself at a molecular level, it will show us more about what humans are made of.
<h6>Tell us about one of your interesting research findings. 
</h6>
One of the most interesting things we’ve been looking at is medical records. We are comparing medical record data with 23andMe surveys, and so far have found the correspondence to be very high. People who fill out 23andMe surveys tend to provide very accurate responses, and that information corresponds highly enough to medical records that it could be statistically relevant for future studies.
<div style="float: right; text-align: justified; width: 200px; background-color: #eee; padding: 15px; margin-left: 10px;">Chao Tian, PhD Statistical Geneticist 
Education:BA Wuhan University, China 
PhD, Statistical Genetics, UC Davis 
Fun Fact:I write classical Chinese poetry. If I hadn’t chosen science, I would’ve pursued a literature degree.</div>
Last year I also presented a paper at <a href="https://blog.23andme.com/23andme-research/23andme-at-ashg/">ASHG</a> called, “<a href="https://blog-api.23andme.com/wp-content/uploads/2013/10/GWAS-for-Susceptibility-to-Infection.pdf">GWAS Identifies Classical HLA Alleles Associated with Susceptibility to Infectious Diseases</a>.” For that research, we studied 23 infectious diseases like chickenpox, shingles, strep throat and mumps etc. to find associated proteins and alleles. The results of the study could impact future vaccine design and disease preventions.
<h6>What interesting thing have you learned about yourself from being tested? 
</h6>
I’ve learned that we need more data. As an Asian person, I received different results from the 23andMe test than most of our European customers. As we get more data from our customers, we’ll be able to improve our results to reflect the diverse culture here in the US. I can just imagine the sheer value of having millions of phenotypes – especially across a diverse range of ethnicities. Once we have bigger sample sizes, we’ll be able to repeat a lot of the studies traditionally done on Europeans for people with diverse backgrounds.
<h6>Tell us about a recent breakthrough in genetics research that you think will have a big impact. </h6>

<a href="https://blog.23andme.com/health-traits/talking-about-breast-cancer-risk/">Angelina Jolie’s decision</a> to undergo a double mastectomy, due to her genetic risk of breast cancer and family history of the disease, brought a lot of attention to genetics. Currently available BRCA tests can now easily test for the rare variant mutations in the breast cancer gene with incredible accuracy. In the future we’ll be able to bring that level of accuracy into testing for other diseases, and that’s very important.
<h6>What&#8217;s one thing the average person should know about genetics? 
</h6>
Genetics is important. It can determine if you’re at high risk for certain conditions and enable you to take action to prevent that.

A Conversation With 23andMe Researcher Chao Tian

<img loading="lazy" decoding="async" class="alignright size-full wp-image-3694" title="istock_000005872885xsmall" src="https://blog-api.23andme.com/wp-content/uploads/2009/05/istock_000005872885xsmall.jpg" alt="" width="328" height="246" srcset="https://blog.pub.us-west-2.prd.23andme.us/wp-content/uploads/2009/05/istock_000005872885xsmall.jpg 400w, https://blog.pub.us-west-2.prd.23andme.us/wp-content/uploads/2009/05/istock_000005872885xsmall-300x225.jpg 300w" sizes="auto, (max-width: 328px) 100vw, 328px" />
Having a particular immune system marker greatly increases a person&#8217;s risk of developing liver failure in response to a common antibiotic, a new study reports.
Drug-induced liver injury accounts for more than half of the approximately 2,000 cases of acute liver failure in the United States each year.   Most of this is due to acetaminophen (Tylenol ®), but a range of other drugs can also present a danger.   One of these, flucloxacillin (also called floxacillin), an antibiotic commonly used to treat staphylococcal infections, leads to liver failure within the first 45 days of treatment in an estimated 8.5 out of every 100,000 people taking the drug.
So far, it has been unknown what makes someone more or less susceptible to flucloxacillin-induced liver damage.   But now an international team of researchers has shown that an immune system variation may be the key.   Their results, published online yesterday in the journal <a href="https://dx.doi.org/10.1038/ng.379" target="_blank" rel="noopener noreferrer">Nature Genetics</a>, show that having one or two Gs at increases the odds of drug-induced liver injury in response to flucloxacillin by at least 45 times compared to having two Ts at this SNP.
A G at indicates the presence of an immune marker known as HLA-B*5701.   This same marker has been linked to <a href="https://www.ncbi.nlm.nih.gov/pubmed/18303141?ordinalpos=1&amp;itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_DefaultReportPanel.Pubmed_RVDocSum" target="_blank" rel="noopener noreferrer">hypersensitivity to the HIV drug abacavir</a>, although the researchers say that adverse reactions to flucloxacillin and abacavir may be the result of different biological mechanisms.
HLA-B*5701 is usually found only in people with European ancestry. Approximately 5% of people in this group have one or two copies of the marker.   The authors of the study speculate that because people with Asian and African ancestry rarely carry HLA-B*5701, their risk for drug-induced liver injury in response to flucloxacillin might also be lower, although there is not data for this yet.
The authors conclude that testing for HLA-B*5701 in people suspected of having flucloxacillin drug-induced liver injury could be useful.   If prompt testing were available, they say, alternative drugs such as cloxacillin and dicloxacillin could be substituted for flucloxacillin.   According to their data, an estimated 85% of cases would prove to be HLA-B*5701-positivie.
But, they warn, testing for HLA-B*5701 before administering flucloxacillin would probably not be clinically useful or cost-effective because only one out of every 500 to 1,000 people with the HLA-B*5701 marker is predicted to have liver problems when treated with the drug.

adverse drug reaction

A Big Step Forward for Patient Safety

A Conversation With 23andMe Researcher Chao Tian

Genetic Variation In Immune System Marker May Increase Risk of Liver Injury From Common Antibiotic

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