DPD Biomarker

DPYD is the gene carrying the instructions for making the dihydropyrimidine dehydrogenase (DPD) protein.  

Wild type DPD protein is an enzyme that breaks down pyrimidines (uracil, a nucleotide in RNA and thymidine, a nucleotide in DNA). In CRC patients, the wild type DPD protein breaks down fluoropyrimidine drugs (like 5-fluorouracil or 5-FU) including when given in combinations (like FOLFOX or FOLFIRI) from toxic to non-toxic molecules.

Mutations in DPYD lead to reduced activity of the DPD protein (partial deficiency) or complete loss of the DPD protein activity. Patients with DPYD mutations cannot break down fluorouracil- or fluoropyrimidine-based chemotherapies. Therefore, DPYD mutations indicate if a person is more likely to experience toxicity at usual doses of 5FU, which might warrant dose reductions—or in some cases—inability to safely give the drug. 

Partial DPD deficiency usually is asymptomatic until a patient is treated using a fluorouracil- or fluoropyrimidine-based chemotherapy. Therefore, DPYD mutations indicate if a person is more likely to experience toxicity at usual doses of 5FU, which might warrant dose reductions—or in some cases—inability to safely give the drug.

Patients with a less-efficient DPD protein are often called intermediate metabolizers – they have some functional protein to metabolize (break down) fluorouracil- or fluoropyrimidine-based chemotherapies. These patients who are treated with fluorouracil- or fluoropyrimidine-based chemotherapies may experience severe side effects, such as neutropenia (low white blood cell count), diarrhea, and inflammation of the gastrointestinal tract.  

Patients with no DPD protein activity may have life-threatening complications.  

Mutations in DPYD are rare. Only 2-8% of the world’s population has a DPYD mutation that causes partial DPD deficiency. Complete loss of DPD activity is even more rare – it only occurs in less than 0.5% of the world’s population (these mutations often lead to other problems that are diagnosed early).  

Testing for DPYD mutations or DPD protein deficiency is not as common as other biomarker testing and there are no standardized recommendations. Patients generally only get tested after experiencing severe toxicity during treatment. If you are experiencing severe side effects during fluorouracil- or fluoropyrimidine-based chemotherapy treatment, you should speak with your medical care team immediately. 

Testing for DPYD mutations before starting treatment only identifies about half of the patients who will develop chemotherapy toxicity. The remaining half are a result of adverse effects not associated with DPD. It is best to speak with your medical team to determine whether testing before treatment would benefit you.  

This biomarker testing requires a blood sample or a collection of cells from your mouth or saliva. This testing looks at your cells (not your tumor cells) for mutations or protein levels/activity.  

Mutations in the DPYD gene are usually hereditary.  

If you have a DPYD mutation that causes partial DPD deficiency, you have an increased risk for toxicity as a result of chemotherapy treatment. Your medical team may recommend a reduced dose of fluorouracil- or fluoropyrimidine-based chemotherapies (as recommended by the Clinical Pharmacogenetics Implementation Consortium). However, if severe toxicity occurs, your medical team may recommend changing your regimen to avoid fluorouracil- or fluoropyrimidine-based chemotherapies.  

If you have a DPYD mutation that causes partial DPD deficiency, you have an increased risk for toxicity as a result of chemotherapy treatment. Your medical team may recommend a reduced dose of fluorouracil- or fluoropyrimidine-based chemotherapies (as recommended by the Clinical Pharmacogenetics Implementation Consortium). However, if severe toxicity occurs, your medical team may recommend changing your regimen to avoid fluorouracil- or fluoropyrimidine-based chemotherapies.