High Amphiregulin and Epiregulin expression in K-ras wild type colorectal primaries predicts response and survival benefit after treatment with cetuximab and irinotecan for metastatic disease

B103 To date no validated markers of outcome to cetuximab (CTX) in metastatic colorectal cancer (CRC) exist. The potential use of molecular markers determined on the primary tumor needs to be explored. We determined the KRAS mutation (Mut) state and measured the EGFR ligands’, Amphiregulin (AR) and Epiregulin (ER), mRNA expression levels in 95 Formalin Fixed Paraffin embedded (FFPE) primary CRC specimens of patients (pts) treated with CTX standard dose and Irinotecan (IRI) in clinical trials for metastatic disease and correlated these variables with response and overal survival (OS).
 Methods
 Tumor areas were manually dissected for RNA and DNA extraction. AR and ER mRNA expression was assessed by real-time quantitative RT-PCR (TaqMan). Expression levels (ΔCt ) represent the average value of duplicate reactions, normalized for GAPDH expression. Lower ΔCt values indicate higher expression. The median ΔCt value was used as cut-off between high and low expression. KRAS exon 2 Mut were analyzed by allele specific TaqMan and confirmed by PCR and sequencing. RECIST criteria for tumor response were used.
 Results The expression of AR and ER in these primaries showed a normal distribution. Mean ΔCt was 4.516 (SD 1.493) (95%CI 4.211-4.820) for AR and 4.797 (SD 1.588) (95%CI 4.473-5.120) for ER. AR and ER expression were significantly correlated (r =0.712 , p Discussion We show that AR and ER mRNA expression can be quantified on FFPE primary tumor samples. Only in KRAS WT pts they significantly influence tumor response and OS, when subsequent metastatic disease is treated with CTX and IRI. The identification of these response predictors early on in the disease process and their persistence in metastases (1), suggests AR, ER and KRAS mutation status are essential players in tumor biology and stresses the importance of the EGF pathway in this setting. The combined use of these markers on primary tumors may provide an improved prediction of outcome so far in mCRC treated with CTX and IRI.
 (1)Khambata-Ford S et al. J Clin Oncol 2007;25(22):3230-7