Dose Individualization of Chemotherapy in Patients With Gastrointestinal Cancers Lacking a Specific Liver Enzyme

Inclusion Criteria:

1. Patients with pre-treatment screening based on [U] value according to INCa/HASrecommendations.

2. Eastern Cooperative Oncology Group performance status (ECOG PS) ≤2

3. Fluoropyrimidine-naïve patients with gastrointestinal cancer starting chemotherapycombining fluoropyrimidine (5-FU or capecitabine) and oxaliplatin whatever thecontext (adjuvant, neoadjuvant, palliative) including the following regimens (themost frequently prescribed in gastrointestinal cancers):

• biweekly 5-FU and oxaliplatin (FOLFOX) +/- targeted therapy (TT)

• three-weekly capecitabine and oxaliplatin (CAPOX) +/- TT

4. Age ≥ 18 years

5. Patients eligible for full standard fluoropyrimidine and oxaliplatin dosesregardless of DPD deficiency

6. Adequate bone marrow function (cell blood count (CBC)), estimated glomerularfiltration rate (DFG) ≥ 50 ml/min, alkaline phosphatase (ALP) / aspartateaminotransferase (ASAT) / alanine aminotransferase (ALAT) ≤ 5 upper limit of normal (ULN), and bilirubin ≤ 50 micromol/L

7. Patient must have signed and dated a written informed consent form prior to anytrial specific procedures. When the patient is physically unable to give theirwritten consent, a trusted person of their choice, independent from the investigatoror the sponsor, can confirm in writing the patient's consent.

8. Women of childbearing potential must have a negative serum or urine pregnancy test.

9. Patients must agree to remain abstinent or use contraceptive methods with a failurerate of < 1% per year for the duration of study treatment and within 6 months aftercompleting treatment.

10. Patients must be affiliated to a Social Security System (or equivalent).

11. Patient is willing and able to comply with the protocol for the duration of thetrial including undergoing treatment and scheduled visits, and examinationsincluding follow-up.

Exclusion Criteria:

1. Patients with complete DPD deficiency based on [U] ≥150 ng/mL

2. Any prior treatment including a fluoropyrimidine

3. Patients with any contraindication to treatment with fluoropyrimidine or oxaliplatinregardless of DPD deficiency

4. Patients not eligible for full standard dose fluoropyrimidine and oxaliplatin forclinical reasons including older age and/or comorbidity regardless of a DPDdeficiency

5. Patients unwilling or unable to comply with trial obligations for geographic,social, or physical reasons, or who are unable to understand the purpose andprocedures of the trial

6. Recent or concomitant treatment with brivudine

7. Pregnant or breastfeeding woman.

8. Participation in another therapeutic trial within 30 days prior to inclusion.

9. Persons deprived of their liberty or under protective custody or guardianship.