Author(s): Amado RG, Wolf M, Peeters M, Van Cutsem E, Siena S,
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Abstract PURPOSE: Panitumumab, a fully human antibody against the epidermal growth factor receptor (EGFR), has activity in a subset of patients with metastatic colorectal cancer (mCRC). Although activating mutations in KRAS, a small G-protein downstream of EGFR, correlate with poor response to anti-EGFR antibodies in mCRC, their role as a selection marker has not been established in randomized trials. PATIENTS AND METHODS: KRAS mutations were detected using polymerase chain reaction on DNA from tumor sections collected in a phase III mCRC trial comparing panitumumab monotherapy to best supportive care (BSC). We tested whether the effect of panitumumab on progression-free survival (PFS) differed by KRAS status. RESULTS: KRAS status was ascertained in 427 (92\%) of 463 patients (208 panitumumab, 219 BSC). KRAS mutations were found in 43\% of patients. The treatment effect on PFS in the wild-type (WT) KRAS group (hazard ratio [HR], 0.45; 95\% CI: 0.34 to 0.59) was significantly greater (P < .0001) than in the mutant group (HR, 0.99; 95\% CI, 0.73 to 1.36). Median PFS in the WT KRAS group was 12.3 weeks for panitumumab and 7.3 weeks for BSC. Response rates to panitumumab were 17\% and 0\%, for the WT and mutant groups, respectively. WT KRAS patients had longer overall survival (HR, 0.67; 95\% CI, 0.55 to 0.82; treatment arms combined). Consistent with longer exposure, more grade III treatment-related toxicities occurred in the WT KRAS group. No significant differences in toxicity were observed between the WT KRAS group and the overall population. CONCLUSION: Panitumumab monotherapy efficacy in mCRC is confined to patients with WT KRAS tumors. KRAS status should be considered in selecting patients with mCRC as candidates for panitumumab monotherapy. TRIAL REGISTRATION: ClinicalTrials.gov NCT00113763 NCT00113776.
This article was published in J Clin Oncol
and referenced in Journal of Pharmacogenomics & Pharmacoproteomics