Biomarker Analysis in A Randomized Phase 2 Study of Panitumumab Versus Cetuximab in Colorectal Cancer (WJOG6510GTR)

Background: The randomized phase II WJOG6510G study demonstrated the non-inferiority of panitumumab to cetuximab in terms of progression-free survival (PFS) in patients with wild-type KRAS exon 2 metastatic colorectal cancer. In this study, we performed exploratory analyses of updated survival data using the KRAS exon 2 and RAS/BRAF statuses. Methods: Patients with wild-type KRAS exon 2 metastatic colorectal cancer who experienced progression after the failure of fluoropyrimidine, oxaliplatin, and irinotecan were randomized to receive panitumumab or cetuximab in combination with irinotecan. An independent central laboratory performed RAS/BRAF testing using a PCR-reverse sequence-specific oligonucleotide method. Results: In the updated analysis of 121 enrolled patients after a median follow-up of 31.3 months, the median PFS was 5.4 months in the panitumumab arm, versus 4.3 months in the cetuximab arm (hazard ratio [HR]=0.68). The median overall survival (OS) times were 14.9 and 12.5 months in the panitumumab and cetuximab arms, respectively (HR=0.68). In 83 analyzed patients, RAS/BRAF testing identified 19 (23%) and 4 patients (5%) with RAS and BRAF mutations, respectively. In the wild-type RAS and BRAF population, trends of better PFS (6.5 months versus 4.6 months; HR=0.57) and OS (15.3 months versus 11.8 months; HR=0.77) were observed for panitumumab. Conclusions: In this updated analysis, panitumumab was associated with a modest survival benefit versus cetuximab in patients with centrally confirmed wild-type KRAS exon 2 metastatic colorectal cancer as well as in the wild-type RAS and BRAF population.