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Biomarkers
DPYD
Fast facts:
  • DPYD is a treatment toxicity biomarker
  • DPYD is the gene encoding the DPD enzyme that affects how your body breaks down fluorouracil and capecitabine derived chemotherapy drugs.
  • People with a DPYD mutation that causes them to have a decreased amount of DPD enzyme are at increased risk of severe fluorouracil toxicity.
  • 2-8% of the population has a DPYD mutation causing decreased DPD enzyme.
  • People with decreased DPD enzyme may need to take lower doses of fluorouracil and capecitabine.
  • DPYD testing before beginning fluorouracil or capecitabine treatment may reduce your risk of severe side effects.

What is DPYD?

DPYD is a gene that affects how your body breaks down toxic fluoropyrimidine related chemotherapy drugs (like 5-FU, 5-fluorouracil) into non-toxic forms. 5-FU related chemotherapy is used to treat colorectal cancer because its toxicity kills cancer cells. However, if you do not have enough of the enzyme that breaks down 5-FU, the levels of 5-FU can build up in your body and lead to severe toxic effects.  

DPYD is the gene that encodes an enzyme called “dihydropyrimidine dehydrogenase” or DPD. That means that the DPYD gene gives your cells the instructions to make the DPD enzyme. The DPD enzyme is needed to break down (metabolize) 5-FU related chemotherapy drugs in your body. Mutations in the DPYD gene can cause DPD enzyme deficiency, that is, they can reduce the amount or activity of your DPD enzyme.

DPD deficiency can be partial (reduced DPD enzyme activity) or complete (no DPD enzyme activity). When your healthcare team talks about DPYD as it is related to cancer treatment, they are talking about partial DPD deficiency. 2-8% of the world’s population has a DPYD mutation causing decreased DPD (partial deficiency). Partial DPD deficiency usually causes no symptoms and only becomes known when a person has genetic testing or has severe toxic effects from 5-FU related chemotherapy. (Complete DPD deficiency is very rare. It occurs in less than 0.5% of people, and usually causes neurologic (brain-related) problems that are diagnosed in infancy.)

DPYD mutations are important because they affect your risk of treatment side effects. If you have a DPYD mutation causing decreased DPD enzyme, fluoropyrimidine chemotherapy drugs are not broken down properly, leading to increased levels of 5-fluorouracil (5-FU) in your body. Increased 5-FU levels can lead to severe toxicity and even life-threatening toxic effects.  

Mutations in the DPYD gene are hereditary. If a family member has a DPYD mutation causing partial DPD enzyme deficiency, it will not affect their health unless they are given 5-FU related chemotherapy at some point in their lives. DPYD mutations do not cause colorectal cancer, and colorectal cancer does not cause DPYD mutations.

Testing for DPYD mutation before starting treatment with 5-fluorouracil related chemotherapy identifies about 50% of the patients who will develop severe toxicity from 5-FU. The other 50% of people who develop severe toxicity have those adverse effects for reasons not related to DPYD and the DPD enzyme.  

How is DPYD tested?

When testing for DPYD, your medical team is looking specifically at your genes and/or enzyme levels, not your tumor’s genes and enzymes. DPYD is tested in a blood sample or in cells collected from your mouth or saliva.

DPYD can be tested by looking at the DNA sequence of the gene to look for a mutation (genotyping). It can also be tested by measuring the DPD enzyme level or activity to look for reduced amounts or reduced function (phenotyping).

Both genotyping and phenotyping are good ways to determine whether your DPYD status puts you at high risk for severe 5-FU toxicity.

What do my DPYD test results mean?

For a DPYD phenotype test, your results will be reported as normal DPD enzyme activity, decreased DPD enzyme activity (partial DPD deficiency), or absent DPD enzyme activity (complete DPD deficiency).

For a DPYD genotype test, your results may be reported as “DPYD wild-type” which means you have no DPYD mutation. Or, if you do have a DPYD mutation causing DPD deficiency, your results will be reported as “DPYD mutant” and may list the specific mutation found.

How do my DPYD results impact my treatment?

If your DPYD genetic testing result is wild-type (WT) or your DPD enzyme level is normal

  • You are at average risk of severe toxicity from 5-FU related drugs.
  • Your treatment can include 5-FU related drugs (5-FU, capecitabine) at the usual doses.

If your DPYD has a mutation that causes decreased DPD enzyme activity (partial DPD deficiency)

  • You have an increased risk of 5-fluorouracil toxicity.  
  • Your oncology team may reduce the dose of your fluoropyrimidine chemotherapy, so that the levels of 5-FU in your body are high enough to kill cancer cells, but not so high that they cause severe toxicity. Guidelines for dose reduction are available from the CPIC.
  • If severe toxicity occurs, your healthcare team may change your chemotherapy regimen to avoid 5-FU related drugs.

Who should be tested for DPYD?

All colorectal cancer patients who experience severe toxicity from 5-fluorouracil related chemotherapy (5-FU, FOLFOX, FOLFIRI, capecitabine) should be tested for DPYD mutations or DPD enzyme deficiency.  

Recommendations for pre-treatment DPYD testing are different around the world. For example, the U.S. Food and Drug Administration recommends physicians discuss DPYD testing with patients before taking floropyrimidine drugs. Talk to your healthcare team about whether pre-treatment testing would benefit you.

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Key Terms
5-Fluorouracil

A fluoropyrimidine drug that is used to treat cancer. It is a conventional chemotherapy drug. It kills cancer cells by disrupting their ability to make and repair DNA.

5-Fluorouracil
A fluoropyrimidine drug that is used to treat cancer. It is a conventional chemotherapy drug. It kills cancer cells by disrupting their ability to make and repair DNA.
Capecitabine (Xeloda)

A fluoropyrimidine drug that is used to treat cancer. It is a conventional chemotherapy drug. It kills cancer cells by disrupting their ability to make and repair DNA.

Capecitabine (Xeloda)
A fluoropyrimidine drug that is used to treat cancer. It is a conventional chemotherapy drug. It kills cancer cells by disrupting their ability to make and repair DNA.
CAPOX regimen

capecitabine + oxaliplatin. Also known as CAPEOX regimen.

CAPOX regimen
capecitabine + oxaliplatin. Also known as CAPEOX regimen.
FOLFOX regimen

folinic acid (leucovorin calcium) + 5-fluorouracil (5-FU) + oxaliplatin

FOLFOX regimen
folinic acid (leucovorin calcium) + 5-fluorouracil (5-FU) + oxaliplatin
FOLFIRI regimen

folinic acid (leucovorin calcium) + 5-fluorouracil (5-FU) + irinotecan

FOLFIRI regimen
folinic acid (leucovorin calcium) + 5-fluorouracil (5-FU) + irinotecan
Pharmacodynamic biomarker

A biomarker that gives information about how your body metabolizes certain drugs. In the setting of colorectal cancer treatment, pharmacodynamic biomarkers give information about what treatments may cause severe side effects.

Pharmacodynamic biomarker
A biomarker that gives information about how your body metabolizes certain drugs. In the setting of colorectal cancer treatment, pharmacodynamic biomarkers give information about what treatments may cause severe side effects.
Toxicity

The quality or extent of being poisonous or harmful. In the setting of cancer treatment, it is used to describe the severe side effects of a treatment.

Toxicity
The quality or extent of being poisonous or harmful. In the setting of cancer treatment, it is used to describe the severe side effects of a treatment.

What is a biomarker?

A biomarker is a piece of information about your health. Biomarkers include your blood pressure, your blood type, and cholesterol or blood sugar levels measured in a blood test. The biomarkers of cancer are also known as tumor markers.