FOLFIRINOX-R is a prospective, multicentric, non-randomized, open-label, phase 1b/2 trial conducted at four cancer centers in France. It had a standard 3 + 3 design for dose escalation followed by a phase 2 trial to study the safety and efficacy of regorafenib in combination with FOLFIRINOX after identification of the recommended phase 2 dose (RP2D). The study details have been previously reported [18].

Key inclusion criteria were: ≥18-year-old patients with an Eastern Cooperative Oncology Group (ECOG) performance status of ≤ 1, with measurable (according to RECIST version 1.1) and unresectable mCRC and RASm by circulating tumor DNA analysis. In addition, patients should not have been previously treated for mCRC. Patients needed to have adequate bone marrow, renal and liver functions, serum lipase ≤ 1.5 times the upper limit of normal (ULN), serum uracil < 17 ng/ml, and wild type homozygous or heterozygous status for the uridine diphosphate glucuronosyltransferase (UGT) 1A1*28 polymorphism [18]. Patients with the UGT1A1*28/*28 genotype were not selected in this FOLFIRINOX-R study.

The study was conducted following the principles of the Declaration of Helsinki and the International Conference on Harmonization and Good Clinical Practice guidelines. The study protocol (ClinicalTrials.gov identifier: NCT03828799), including all amendments, was reviewed and approved by the French ethics committee (CPP Est III) on December 4, 2018, and the French National Agency for the Safety of Health Products (ANSM) on November 21, 2018. Patients provided their written informed consent before enrollment in the study.

FOLFIRINOX was administered as per standard: oxaliplatin 85 mg/m² on day 1 (intravenous, IV, infusion over 2 h), immediately followed by folinic acid 400 mg/m² or calcium levofolinate 200 mg/m² (2-hour IV infusion), with the addition of irinotecan (150 or 180 mg/m² ; 90-minute IV infusion through a Y-connector) immediately followed by 5-fluorouracil (400 mg/m² IV bolus then 2400 mg/m² over 46 h continuous infusion) (19). Primary prophylactic granulocyte colony-stimulating factor (G-CSF) was delivered from day 7 to day 12. Regorafenib was administered orally (80, 120, or 160 mg) once per day from day 4 to day 10 of each 14-day cycle. The pre-defined dose levels (DLs) were as follows: DL -1 (irinotecan 150 mg/m² plus regorafenib 80 mg/m²); DL1 (irinotecan 150 mg/m² plus regorafenib 120 mg/m²); DL2 (irinotecan 180 mg/m² plus regorafenib 120 mg/m²); and DL3 (irinotecan 180 mg/m² plus regorafenib 160 mg/m²). Treatment cycles were repeated every 14 days for up to 12 cycles. Then, treatment continued with a maintenance phase (regorafenib alone) until disease progression, unacceptable toxicity, or consent withdrawal. Details on permitted dose delays and modifications were provided in the already published study protocol [18]. Specifically, treatment could be interrupted to perform surgical resection or any regional procedure, if needed. Laboratory and clinical evaluations were performed at each cycle (see reference 18 for more details). During the first three cycles, laboratory assessments were performed also on day 8 of each cycle. Tumor assessment (RECIST, v1.1) was performed every 8 weeks. The main objective of the phase 1 of this study was to determine the maximum tolerated dose (MTD) and the RP2D of the combination of regorafenib plus FOLFIRINOX by testing different doses of regorafenib and irinotecan. The dose-limiting toxicity (DLT) period was defined as the time from the first cycle of treatment until the day of the planned fourth cycle, corresponding to 42 days. DLT was defined as the occurrence of one or more of the following toxicities during the first three cycles of treatment: any unplanned interruption > 7 days of regorafenib due to drug-related toxicity, grade ≥ 3 (CTCAE v5) non-hematologic toxicity (except grade 3 nausea, grade 3 vomiting, grade 3 diarrhea and grade ≥ 3 lipase elevation without signs of pancreatitis), grade ≥ 2 posterior reversible encephalopathy syndrome, grade ≥ 2 retinopathy, any of the following liver-specific toxicities [grade ≥ 3 bilirubin increase, grade ≥ 3 aspartate transaminase (AST) and/or alanine transaminase (ALT) increase, or AST and/or ALT increase > 3 x ULN with concurrent bilirubin increase > 2 x ULN], grade 4 neutropenia lasting > 3 days, grade ≥ 3 febrile neutropenia, grade 4 anemia, platelets < 25,000 /mm3 or platelets < 50,000 /mm3 with bleeding, grade ≥ 3 international normalized ratio or partial thromboplastin time elevation with bleeding, grade ≥ 3 hemorrhage/bleeding. The phase 2 part of the study would start after the RP2D determination and after the agreement by the Independent Data Monitoring Committee (IDMC). The primary objective of the phase 2 study was to evaluate the 48-week disease-control rate in all treated patients. The main secondary endpoints of the study included safety according to the NCI-CTCAE v.5, ORR according to the RECIST v1.1, deepness of response, disease control rate (DCR), PFS, and overall survival [18].

A minimum of 12 and a maximum of 24 patients needed to be included in the phase 1 study, with a minimum of 3 and a maximum of 6 patients per DL. Six patients needed to be included at the RP2D. The phase 2 part of the trial followed a Fleming’s one-stage design. Detailed assumptions and numbers of patients to be included were described in Adenis et al. [18].