5-Fluorouracil Sensitivity

Diagnosis

Indications for Testing

  • Predict toxicity and responsiveness of tumor to 5-fluorouracil (5-FU) therapy

Laboratory Testing

  • 5-FU response testing
    • DPYD and TYMS gene mutations detected that may increase risk for 5-FU toxicity and predict responsiveness to 5-FU therapy
      • Alternative chemotherapeutic agents, therapeutic drug monitoring, altered 5-FU doses, or increased surveillance for adverse drug reactions may be indicated

Clinical Background

5-fluorouracil (5-FU) is a fluoropyrimidine drug and the most frequently used chemotherapeutic in the treatment of colorectal cancer. Genetic mutations in the DPYD and TYMS genes may predict the risk of 5-FU toxicity, responsiveness to 5-FU therapy, and clinical outcome to aid in patient care.

Genetics and Epidemiology

  • Mutations, allele frequency, and predicted consequences

    Mutations, Allele Frequency, and Predicted Consequences

    DYPD Gene Mutations

    DYPD mutation (alternative name[s])

    Allele Frequency in Indicated Population

    Predicted Consequences in Patients Receiving 5-FU

    c.1679T>G (DPYD*13, rs55886062)

    0.1% – French Caucasian

    Decreased DPD activity

    Increased toxicity risk

    c.1905+1G>A (DPYD*2A, IVS14+1G>A, rs3918290)

    0.47-2.2% – Dutch, German, French, Turkish, Finnish

    Absent – Japanese, Korean, African American

    Abolished DPD activity

    Greatly increased toxicity risk

    c.2846A>T (rs67376798)

    1.0% – French Caucasian

    Decreased DPD activity

    Increased toxicity risk

    TYMS Gene Mutations

    TYMS mutation (alternative name[s])

    Allele Frequency in Indicated Population

    Predicted Consequences in Patients Receiving 5-FU

    3'-UTR

    6 bp deletion (TTAAAG) (rs34489327, rs163430)

    DELETION

    29.5% – Caucasian

    Decreased TYMS expression

    Increased 5-FU responsiveness

    Increase risk of toxicity

    INSERTION

    (wild type)

    70.5% – Caucasian

    Increased TYMS expression

    Decreased 5-FU responsiveness

    Decreased risk of toxicity

    5'-TSER

    28bp VNTR (2R; 3R)

     (rs34743033

    G>C SNP in 2nd repeat of 3R allele (3RC) (rs2853542)

    2R

    41-48% – Caucasian, Hispanic, African American

    19% – Chinese

    17.5% – Japanese

    2R/3RG

    • Increased TYMS expression
    • Decreased 5-FU responsiveness
    • Poor prognosis

    2R/2R or 2R/3RC

    • Decreased TYMS expression
    • Increased 5-FU responsiveness
    • Increased risk of toxicity

    3RG

    51% – Chinese

    42.7% – Japanese

    26-37% – Caucasian, Hispanic, African American

    3RG/3RG, 3RG/3RC, or 2R/3RG

    • Increased TYMS expression
    • Decreased 5-FU responsiveness
    • Poor prognosis

    3RC

    39.9% – Japanese

    30% – Chinese

    15-33% – Caucasian, Hispanic, African American

    3RG/3RC

    • Increased TYMS expression
    • Decreased 5-FU responsiveness
    • Poor prognosis

    3RC/3RC or 2R/3RC

    • Decreased TYMS expression
    • Increased 5-FU responsiveness
    • Increased risk of toxicity

Pathophysiology

  • Dihydropyrimidine dehydrogenase (DPD) enzyme – encoded by DPYD gene
    • Catabolizes approximately 80% of 5-FU into an inactive form that is eliminated in the urine
    • Reduced DPD activity can lead to the accumulation of active 5-FU metabolite, increasing the risk for 5-FU toxicity
  • Thymidylate synthase (TYMS) enzyme – encoded by TYMS gene
    • Primary target for 5-FU
      • Remaining 5-FU drug is metabolized by different enzymes into an active form that inhibits the synthesis of DNA and RNA by competitive inhibition of TYMS or by direct incorporation of cytotoxic metabolites into nucleic acids
    • TYMS gene mutations result in reduced expression of TYMS and may be associated with higher clinical responsiveness to 5-FU therapy and increased risk of toxicity

Clinical Presentation

  • Grade III-IV toxicity (occurs in ~16% of treated patients)
    • Mucositis
    • Neutropenia
    • Nausea
    • Diarrhea
    • Neurological symptoms

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
5-Fluorouracil (5-FU) Toxicity and Chemotherapeutic Response, 5 Mutations 2007228
Method: Polymerase Chain Reaction/Single Nucleotide Extensions/Fragment Analysis

Predict toxicity and responsiveness of tumor to 5-FU therapy

Clinical sensitivity – estimated at 31% for the DPYD variants analyzed

Analytical sensitivity/specificity – 99%

Only targeted mutations in the DPYD and TYMS genes are evaluated

Rare diagnostic errors may occur due to rare sequence variations

Genetic and/or non-genetic factors that are not detected by this assay may affect 5-FU drug metabolism, efficacy, and risk for toxicity

Genotyping does not replace the need for therapeutic drug monitoring or clinical observation

Lack of detection of the targeted DPYD and TYMS mutations does not rule out risk for 5-FU toxicity or predict degree of responsiveness to 5-FU

 
Dihydropyrimidine Dehydrogenase (DPYD), 3 Mutations 2012166
Method: Polymerase Chain Reaction/Single Nucleotide Extensions/Fragment Analysis

Predicts risk of toxicity to 5-FU therapy due to impaired metabolism

Clinical sensitivity – ~31% for DPYD variants analyzed

Analytical sensitivity/specificity – 99%

Only targeted mutations in DPYD gene will be detected

Rare diagnostic errors may occur due to rare sequence variations

Genetic and/or non-genetic factors that are not detected by this assay may affect 5-FU drug metabolism, efficacy, and risk for toxicity

Genotyping does not replace the need for therapeutic drug and clinical monitoring

Lack of detection of the targeted DPYD mutations does not rule out risk for 5-FU toxicity or predict degree of responsiveness to 5-FU