Background: Adjuvant chemotherapy is the current worldwide standard of care for stage III colorectal cancer (CRC) but it leads to significant neurotoxicity. We have shown in 2 cohorts of CRC patients treated with Oxaliplatin (Ox) that Ox-due neuropathy occurred in patients receiving an excess of 3.09 mg Ox/ kg Lean Body Mass (LBM). The aim of this trial was to determine whether the Ox dose adaptation based on the LBM index can reduce neurotoxicity, in patients treated for a stage III CRC. Methods: LEANOX is a randomized phase II multicentre study in patients eligible for an Ox regimen as adjuvant chemotherapy for CRC. Patients without sarcopenia (LBM index <3.09mg/kg, group 1) received a dosage of Ox according to Body Surface Area (BSA) (85 mg/m²).Patients with sarcopenia (LBM index ≥3.09mg/kg) were randomized in 2 groups, group 2: dosage of Ox according to BSA (similar to group 1) and group 3: a dosage of Ox according to LBM (3.09 mg Ox/ kg LBM). Randomization (1:1) was stratified by center, age and weight loss. The primary endpoint was the percentage of patients without grade ≥2 neurotoxicity during the first 6 cycles of adjuvant Ox-based chemotherapy. The study required 108 randomized patients (bilateral α=0.05, 80% power) to compare the primary endpoint between groups 2 and 3 with P2=55% and P3=80%. Secondary endpoints included time to onset of grade≥2 chronic cumulative neurotoxicity, duration of the chronic cumulative neurotoxicity, cumulative Ox doses that can be delivered without reaching the dose-limiting chronic neurotoxicity, tolerance, disease free survival, overall survival and quality of life. Results: A total of 160 patients were included in 18 french centers: 33 in group 1, 64 in group 2 and 63 in group 3. Median age was 63 years, 52.5 % male, 89.3 % OMS 0 and tumoral stage was T3 (57.5%), T4 (33.8%), N1 (60.6%) and N2 (38.1%). Grade 3-4 AE events occurred in 58.0% in group 2 and 59.7% in group 3. The percentage of patients without experiencing grade ≥ 2 of neurotoxicity during the first 6 cycles of adjuvant Ox-based chemotherapy was 43.9% in group 2 vs 67.2% in group 3 (p=0.01). Conclusions: We wish to avoid severe adverse reactions to Ox regimen by personalization of cancer chemotherapy. Clinical trial information: NCT03255434.