Background: The phase 3 ASPECCT trial in patients (pts) with chemorefractory wild type (WT) KRAS exon 2 metastatic colorectal cancer (mCRC) demonstrated that panitumumab (pmab) was noninferior to cetuximab (cmab) for overall survival (OS). A previous subgroup analysis of hazard ratios (HRs) suggested that pts who had received prior bevacizumab (bev; any line, at any point before study start) in the pmab arm may have had better outcomes vs pts in the cmab arm (Price et al. Lancet Oncol 2014;15:569). Methods: Pts were randomized 1:1 to receive pmab or cmab. The subset of pts who had received prior bev were analyzed based on the final analysis of ASPECCT. Results: 999 pts were randomized and treated: 499 pmab and 500 cmab. The prior bev subset included 126 pts in the pmab arm (25%) and 132 pts in the cmab arm (26%). Pts in the pmab arm had longer median OS and progression-free survival (PFS) and higher objective response rates (ORR) compared with pts in the cmab arm. Results are shown (table). After adjustment for baseline covariates including ECOGperformance status, number of metastatic sites, and baseline lactate dehydrogenase (LDH), OS hazard ratio (HR) was 0.65 (95%CI=0.49-0.85) with pmab vs cmab in pts who had received prior bev. Pts in the pmab and cmab arms who did not receive prior bev had similar OS, PFS, and ORR. Post-progression antitumor therapy was similar between the pmab (47%) and cmab arms (52%) in pts who received prior bev. Conclusions: In ASPECCT, pts with WT KRAS exon 2 mCRC who received prior bev-containing regimens may have derived greater benefit with pmab versus cmab monotherapy. Clinical trial information: NCT01001377

*Evaluable pts.