Background: Aflibercept (AF), a recombinant fusion protein, is a potent inhibitor of vascular endothelial growth factor. This study assessed the safety, dose limiting toxicities (DLTs), recommended dose (RD), and the pharmacokinetics (PK) of AF in combination with FOLFIRI. Methods: This was an open-label, sequential-cohort, dose-escalation study of intravenous AF administered every 2 weeks, in combination with FOLFIRI (fixed doses) in patients (pts) with metastatic colorectal cancer (MCRC). Two dose levels (DL) of AF (2 and 4 mg/kg) were set, and 3-6 pts were to be recruited in each DL. DLTs were to be evaluated in the first 2 cycles. RD was defined as the highest AF dose at which <33% of all evaluable pts experienced DLTs. After establishment of RD, 10 additional pts were treated at RD. PK of AF, irinotecan, SN38, and 5-FU were studied in cycle 1. Results: 16 pts (3 at 2 mg/kg and 13 at 4 mg/kg) with MCRC were treated (M/F, 10/6; median age, 57.0 [47-69]; and ECOG PS 0/1, 9/7), and all had received prior chemotherapies. A total of 131 cycles of AF + FOLFIRI were administered at the two DLs of AF (2 and 4 mg/kg). No DLT was observed. The most common all-causality grade 3/4 adverse events were neutropenia (75.0 %) including one febrile neutropenia after DLT evaluation period and hypertension (25.0%). There was no major safety issue at the RD. Response rate and progression free survival at RD (N=13 pts) was 7.8% and 7.6 month, respectively. Conclusions: RD was determined as 4 mg/kg in this first clinical study of AF in Japanese pts with MCRC. The combination of AF (4 mg/kg) and FOLFIRI was well tolerated in line with results of prior overseas studies. The PK results in Japanese patients showed similar tendency to those reported in patients from other regions of the world.