Metronomic Chemotherapy in Wilms Tumor (MetroWilms-1906)

Inclusion Criteria: * Patient ≥18 months old and ≤ 17 years old * Relapsed or refractory Wilms tumor, histologically proven at diagnosis * After at least 2 lines of chemotherapy (conventional or high dose, which may include the trial molecules) or after 1 line for high risk relapse for which there would not be any curative therapy. If 1 line for high risk relapse, the enrolment should be confirmed by coordinators. * Radiologically measurable or evaluable disease (visible, target or non-target-lesion on MRI or CT-scan) * Performance status: Karnofsky performance status (for patients \>16 years of age) or Lansky Play score (for patients ≤16 years of age) ≥ 70%. * Able to take oral medication or nasal gastric tube or authorized gastrostomy * Adequate biological criteria: * Neutrophils \> 1000/mm3 ; Platelets \> 75 000/mm3 * Transaminases (ALT/ AST) ≤ 3 times ULN (or ≤ 6 times ULN if liver metastasis); total bilirubin ≤ 2 ULN (except in case of Gilbert's disease) * Creatinine ≤ 1,5 ULN or clearance ≥ 60 mL/ min/ 1,73m2 (In case of doubt, to be confirm by assessment of cystatin ) * Females of childbearing potential must have a negative seric pregnancy test within 7 days prior to initiation of treatment. * Sexually active patients must agree to use adequate and appropriate contraception (at least one highly effective contraception or two complementary methods of contraception), 1 month before beginning of treatment while on trial drug and for 7 months after stopping the trial drug for female patients and after 6 months for male patients. * Written informed consent from parents/legal representative, patient, and age-appropriate assent before any trial-specific screening procedures according to national guidelines. * Patient covered by the French "Social Security" regime Exclusion Criteria: * Prior history of other cancer within 5 years * Chemotherapy or radiotherapy of target lesion within 3 weeks prior to inclusion * Target therapy within less than 5 \* half-life of the substance prior to inclusion * Major surgery within 15 days prior to inclusion * Presence of any NCI-CTCAE v5 grade ≥ 2 cardiac, hepatic, pulmonary or renal toxicity * Severe myelosuppression * Severe peripheral neuropathy (grade ≥ 2) * Fructose intolerance * Inflammatory bowel chronic disease and/or intestinal obstruction * Patients with demyelinating form of Charcot-Marie-Tooth disease * Known active viral hepatitis or known human immunodeficiency virus (HIV) infection or any other uncontrolled infection. * Known hypersensitivity to dacarbazine (DTIC), isotretinoin or to any of the trial drugs, trial drug classes, excipients in the formulation * Hyperlipidemia and hypervitaminosis A * Vaccination with a live attenuated vaccine within 1 month prior to inclusion * Pregnant or breastfeeding patients * Inability to comply with medical follow-up of the trial (geographical, social or psychological reasons)