Background: FOLFOXIRI plus bevacizumab (BEV) is regarded as the standard of care for selected patients (pts) with metastatic colorectal cancer (mCRC), despite the high incidence of neutropenia and diarrhea. The AXEPT phase III study showed that the modified capecitabine (CAP) + irinotecan (IRI) + BEV (CAPIRI+BEV) [CAP 1600 mg/m², IRI 200 mg/m², and BEV 7.5 mg/kgq3wk] treatment was non-inferior to FOLFIRI+BEV, with a lower incidence of hematologic toxicity. We hypothesized that the modified CAPIRI combined with oxaliplatin (OX) and BEV (CAPOXIRI+BEV) would be more feasible than FOLFOXIRI+BEV, without compromising efficacy. Methods: The QUATTRO-II study is an open-label, multicenter, randomized phase II study. In Step 1, the recommended doses (RD) of OX and IRI were investigated as a safety lead-in. In Step 2, pts are randomized to either the RD of CAPOXIRI+BEV or FOLFOXIRI+BEV. In Step 1, four dose levels of CAPOXIRI (fixed dose of CAP 1600 mg/m² and BEV 7.5 mg/kg plus escalated or de-escalated doses of OX and IRI, q3wk) were investigated in a 3+3 manner. A dose level of ≤ 2/6 of dose-limiting toxicity (DLT) cases was expected as the RD. Results: A total of 9 pts (3 at Level 0, 6 at Level 1) were included in Step 1. The baseline characteristics were as follows: the median age was 62 years; 6 were male; 6 presented with a left-sided tumor; 8 had a performance status of 0; all wild type/RAS mutant/BRAF V600E mutant were 8/1/0; and UGT1A1 wild type/*6 single hetero/*28 single hetero were 7/0/2. In Level 0 (IRI 200 mg/m², OX 100 mg/m²), one grade 4 neutropenia and one grade 3 anorexia were observed, but without DLT. In Level 1 (IRI 200 mg/m², OX 130 mg/m²), two grade 4 neutropenia and one grade 3 colitis were observed, with 1 DLT (febrile neutropenia) case, fully recovered without G-CSF administration. No treatment-related deaths were observed. Although dose modifications were needed in 4 of the 6 pts, no further safety concerns related to treatment continuity were observed in the 2^nd or subsequent cycles. Thus, we determined that the dose administered in Level 1 is the RD for Step 2. According to the preliminary efficacy results at 8 weeks after initiating study treatment, 6 pts achieved a partial response (2 in Level 0 and 4 in Level 1). Conclusions: The RD of CAPOXIRI+BEV was 200 mg/m² IRI, 130 mg/m² OX, 1600 mg/m² CAP, and 7.5mg/kg BEV. The randomized phase II Step (Step 2) of QUATTRO-II is ongoing. Clinical trial information: NCT04097444