Safety of Trifluridine/Tipiracil in Patients With Dihydropyrimidine Dehydrogenase Deficiency Diagnosed With Metastatic Colorectal or Gastroesophageal Cancer

Inclusion Criteria: 1. Patient must have signed and dated a written informed consent form prior to any trial specific procedures. When the patient is physically unable to give their written consent, a trusted person of their choice, independent from the investigator or the sponsor, can confirm in writing the patient's consent. 2. Histological or cytological documentation of adenocarcinoma of the colon or rectum or gastroesophageal cancer (lower oesophagus, gastroesophageal junction and gastric) 3. Synchronous or metachronous metastatic colorectal or gastroesophageal cancer 4. Presence of at least one measurable lesion according to RECIST v1.1 5. No prior therapy for metastatic disease 6. known DPD deficiency defined as plasma uracil concentration≥16 ng/ml For plasma uracil concentration \[16-20\[ ng/ml, plasma uracil dosage must be repeated in the 7 days to confirm that plasma uracil concentration ≥16 ng/ml. If the second result is different (i.e; uracil concentration \<16 ng/ml), keep the favourable result, and do not include the patient if only the first plasma uracil concentration≥16 ng/ml. 7. Age ≥18 years 8. Eastern Cooperative Oncology Group (ECOG) performance status ≤1 9. Adequate bone marrow, renal and liver functions as evidenced by the following laboratory requirements within 7 days prior to study treatment initiation: 1. Absolute neutrophil count (ANC) ≥ 1,500/ mm³ without biologic response modifiers such as granulocyte colony-stimulating factor (G-CSF), within 21 days before the start of study treatment 2. Platelet count ≥100,000/mm³, without platelet transfusion within 21 days before the start of study treatment 3. Hemoglobin (Hb) ≥9 g/dL, without blood transfusion or erythropoietin within 21 days before the start of study treatment 4. Serum creatinine ≤1.5 x upper limit of normal (ULN) 5. Glomerular filtration rate as assessed by the estimated glomerular filtration rate (eGFR) ≥50 mL/min per 1.73 m² calculated by the Modification of Diet in Renal Disease (MDRD) abbreviated formula 6. Total bilirubin ≤ 1.5 x ULN 7. Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 2.5 x ULN (≤ 5 x ULN for patients with liver involvement of their cancer) 8. Alkaline phosphatase (ALP) ≤ 2.5 x ULN (≤ 5.0 x ULN for patients with liver involvement for their cancer and/or bone metastases) 9. International normalized ratio (INR) ≤1.5 or prothrombin time (PT) ≤1.5 x ULN Note: Patients on stable dose (dose has not been changed in at least 28 days) of anticoagulation therapy will be allowed to participate if they have no sign of bleeding or clotting and INR / PT and PTT / aPTT test results are compatible with the acceptable benefit-risk ratio at the investigator's discretion. In such case, limits as noted would not apply 10. For women of reproductive potential, negative serum beta human chorionic gonadotropin (β-HCG) pregnancy test obtained within 7 days before the start of study treatment. Women not of reproductive potential are female patients who are postmenopausal or permanently sterilized (e.g., tubal occlusion, hysterectomy, bilateral salpingectomy) 11. For women of childbearing potential and men, agreement to use an adequate contraception for the duration of study participation and up to 7 months following completion of therapy. 12. Willingness and ability to comply with scheduled visits, treatment plan, laboratory tests and other study procedures 13. Affiliation to the Social Security System (or equivalent). Exclusion Criteria: 1. Previous or concurrent cancer that is distinct in primary site or histology from colorectal or gastroesophageal cancer within 5 years prior to study inclusion, except for curatively treated cervical cancer in situ, non-melanoma skin cancer and superficial bladder tumors \[Ta (non invasive tumor), Tis (carcinoma in situ) and T1 (lamina propria invasion)\] 2. Radiotherapy within 28 days prior to first dose of treatment 3. Active cardiac disease including any of the following: 1. Symptomatic Congestive heart failure ≥New York Heart Association (NYHA) class 3 or 4 2. Severe Unstable angina (angina symptoms at rest) 3. Myocardial infarction less than 12 months before first dose of treatment 4. Uncontrolled hypertension (Systolic blood pressure ≥140 mmHg or diastolic pressure ≥ 90 mmHg) despite optimal medical management. 5. Ongoing infection ≥Grade 2 (NCI CTCAE v.5.0) 6. Known history of human immunodeficiency virus (HIV) infection 7. Chronic hepatitis B or C infection (if hepatitis status cannot be obtained from medical records, re-testing is required) 8. Seizure disorder requiring medication 9. Symptomatic metastatic brain or meningeal tumours 10. History of organ allograft 11. Known hypersensitivity to any of the study drugs, study drug classes, or any constituent of the products 12. In case of planned treatment with oxaliplatin: Peripheral neuropathy \>Grade 1 (NCI CTCAE v.5.0) 13. In case of planned treatment with bevacizumab: Major surgical procedure, open biopsy, or significant traumatic injury within 28 days prior to first dose of treatment 14. In case of planned treatment with bevacizumab: Evidence or history of any bleeding diathesis, irrespective of severity. Any hemorrhage or bleeding event ≥CTCAE v 5.0 Grade 3 within 4 weeks prior to the start of study medication 15. In case of planned treatment with trastuzumab or panitumumab or bevacizumab: Interstitial lung disease with ongoing signs and symptoms 16. Inability to swallow oral medication 17. Any uncontrolled malabsorption condition 18. Pregnant or breast-feeding subjects. Women of childbearing potential must have a serum pregnancy test performed a maximum of 7 days before start of treatment, and a negative result must be documented before start of study drug 19. Patients unwilling or unable to comply with the medical follow-up required by the trial because of geographic, familial, social, substance abuse, medical or psychological reasons, or any condition that, in the opinion of the investigator, would interfere with the patient's participation in the study or evaluation of study treatment or interpretation of patient safety or study results 20. Participation in another clinical study with an investigational product during the last 30 days before inclusion 21. Patients who might be interconnected with or dependent on the sponsor site or the investigator 22. Persons deprived of their liberty or under protective custody or guardianship, or legal incapacity or limited legal capacity