Analysis of KRAS/NRAS mutations in phase 3 study 20050181 of panitumumab (pmab) plus FOLFIRI versus FOLFIRI for second-line treatment (tx) of metastatic colorectal cancer (mCRC)

LBA387 Background: Previously, this study showed significant improvement in progression-free survival (PFS) in pmab + FOLFIRI vs FOLFIRI (HR=0.73; 95% CI: 0.59-0.90; p=0.004) and a trend toward improved overall survival (OS; HR=0.85; 95% CI: 0.70-1.04; P=0.12; Peeters et al. JCO 2010). Recently, analysis from 1st-line mCRC PRIME study showed that mutations in RAS genes (KRAS/NRAS exons 2/3/4) predicted a lack of response to pmab (Douillard et al. NEJM 2013). Methods: The primary objective was to assess the tx effect of pmab + FOLFIRI vs FOLFIRI on OS and PFS based on RAS mutation status in the primary analysis population. Bidirectional Sanger sequencing was used to detect mutations in KRAS exons 3, 4 and NRAS exons 2, 3, 4 in patients (pts) with known WT KRAS exon 2 mCRC. Results: In this prospective retrospective analysis, overall RAS ascertainment rate was 85% (n=1008/1186). 18% of the WT KRAS exon 2 pts harbored additional RAS mutations (n=107/597). Efficacy is shown (Table). Tx HR for pts with WT RAS was 0.803 (95% CI: 0.629-1.024; P=0.077) for OS and 0.695 (95% CI: 0.536-0.903; P=0.006) for PFS. Conclusions: Improvements were observed in the tx effect of pmab + FOLFIRI vs FOLFIRI on OS and PFS in the WT RAS group vs the WT KRAS exon 2 group. Pts with MT RAS mCRC are unlikely to benefit by the addition of pmab to FOLFIRI, similar to pts with MT KRAS exon 2 mCRC in this study. These findings are consistent with previously reported outcomes by RAS status and support RAS testing to determine potentially appropriate pts for pmab tx. Clinical trial information: NCT00339183. [Table: see text]