454 Background: Pmab has demonstrated significant improvement in progression-free survival (PFS) in pts with WT KRAS mCRC as 2nd-line tx in a phase III trial comparing pmab + FOLFIRI vs FOLFIRI alone. Here, we describe the results of SPIRITT, a multicenter, randomized phase II study evaluating pmab + FOLFIRI and bev + FOLFIRI in pts with WT KRAS mCRC previously treated with a 1st-line bev + oxaliplatin (Ox)-based chemotherapy regimen. Methods: Pts were randomized 1:1 to pmab 6.0 mg/kg + FOLFIRI Q2W or to bev 5.0 or 10.0 mg/kg + FOLFIRI Q2W. Eligibility criteria included: WT KRAS mCRC, ECOG ≤ 1, no prior irinotecan or anti-EGFR tx, and tx failure of prior 1st-line bev + Ox-based therapy (≥ 4 cycles). The primary endpoint was PFS; secondary endpoints included overall survival (OS), objective response rate (ORR), and safety. No formal hypothesis was tested. Results: 182 pts with WT KRAS mCRC were randomized. All pts received tx. Efficacy results are shown (table). Worst grade of 3/4 adverse events (AE) occur...