A phase II study of bevacizumab in combination with irinotecan plus S-1 as first-line treatment in patients with KRAS mutant-type metastatic colorectal cancer.

676 Background: FOLFIRI+bevacizumab (BV) is considered as a first-line treatment in patients (pts) with metastatic colorectal cancer (mCRC). The FIRIS study showed the non-inferiority of irinotecan plus S-1 (IRIS) to FOLFIRI. Therefore, we conducted a phase II study to evaluate the efficacy and safety of BV in combination with IRIS as first-line chemotherapy for KRAS mutant-type (mt) mCRC (clinical trial information: UMIN000004630). Methods: Eligibility criteria included histologically confirmed mCRC, KRAS mt, no previous chemotherapy, ECOG performance status (PS) of 0/1, and adequate organ function. S-1 was administered at 80 mg/m2 on days 1–14 and irinotecan at 100 mg/m2 on days 1 and 15 every 28 days. BV was administered at 5 mg/kg on days 1 and 15 every 28 days. The primary endpoint was response rate (RR), and the secondary endpoints were progression-free survival (PFS), overall survival (OS), and safety. The sample size was calculated to reject a RR of 25% in favor of a target RR of 50% with a signif...