Predictive biomarkers to improve treatment of metastatic colorectal cancer (mCRC): Outcomes with cetuximab plus FOLFIRI in the CRYSTAL trial.

4068 Background: KRAS oncogene mutation status is predictive of efficacy of cetuximab alone or combined with chemotherapy (CT) in mCRC. Previous data from the phase III CRYSTAL trial showed that adding cetuximab to FOLFIRI in first-line mCRC significantly improved the overall response rate (ORR) and progression-free survival (PFS) in pts with KRAS wild-type (wt) tumors. The serine-threonine kinase BRAF is a direct downstream effector of KRAS. Here, we report the influence of KRAS and BRAF status on mature overall survival (OS) data. METHODS DNA was extracted from archived tumor material where available from randomized pts. KRAS and BRAF mutation status (wt or mutant [mt]) was determined by quantitative PCR. Treatment arms were compared using two-sided log-rank tests (5% significance level) for PFS and OS, and the CMH test for best ORR. RESULTS The KRAS-evaluable cohort (n=540; 64.4% KRAS wt) was similar to the overall ITT group. In KRAS wt pts, adding cetuximab to FOLFIRI significantly increased the odds for tumor response nearly 2-fold, reduced the risk of progression by 32% and extended median OS from 21.0 months (mo) to 24.9 mo (details in Table ). KRAS mt pts did not benefit from cetuximab. Data on the impact of BRAF mutations on cetuximab activity will be presented at the meeting. In the FOLFIRI and cetuximab + FOLFIRI arms, 31.2% and 36.1% of pts, respectively, received no further line of therapy, while 25.4% and 6.2%, respectively, received EGFR antibody therapy. CONCLUSIONS The benefits of adding cetuximab to CT were greater in KRAS wt pts than ITT pts for all clinically relevant endpoints. KRAS is a key biomarker for selecting a targeted therapy combined with standard CT in first-line mCRC. [Table: see text] [Table: see text].