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

The goal of this clinical trial is to test the safety of the trifluridine/tipiracil as replacement of fluoropyrimidines based chemotherapy as first line metastatic colorectal or gastroesophageal cancer regimens in patients with dihydropyrimidine dehydrogenase (DPD) deficiency. The main questions it aims to answer are: * Is this alternative chemotherapy option a better option in term of safety for this type of patients? * Does the combination of treatments improves the overall safety? * Does the combination of treatments improves the progression-free survival, overall survival, objective response rate and disease control rate? * Does the combination of treatment have an effect on quality of life? Participants will: * Receive the trifluridine/tipiracil with oxaliplatin every 14 days, associated with: * Panitumumab or bevacizumab for colorectal adenocarcinomas * Nivolumab or trastuzumab for gastroesophageal adenocarcinomas. * Have a CT-Scan every 2 months until disease progression * Complete Health-related quality of life questionnaire every 2 months for a maximum of 6 months * Participate to the optional translational research: Blood samples fo DPYD genotyping and pharmacokinetic analysis