Clinical relevance of KRAS mutation detection in metastatic colorectal cancer treated by Cetuximab plus chemotherapy

Abstract

The predictive value of KRAS mutation in metastatic colorectal cancer (MCRC) patients treated with cetuximab plus chemotherapy has recently been suggested. In our study, 59 patients with a chemotherapy-refractory MCRC treated with cetuximab plus chemotherapy were included and clinical response was evaluated according to response evaluation criteria in solid tumours (RECIST). Tumours were screened for KRAS mutations using first direct sequencing, then two sensitive methods based on SNaPshot and PCR-ligase chain reaction (LCR) assays. Clinical response was evaluated according to gene mutations using the Fisher exact test. Times to progression (TTP) were calculated using the Kaplan-Meier method and compared with log-rank test. A KRAS mutation was detected in 22 out of 59 tumours and, in six cases, was missed by sequencing analysis but detected using the SNaPshot and PCR-LCR assays. Remarkably, no KRAS mutation was found in the 12 patients with clinical response. KRAS mutation was associated with disease progression (P=0.0005) and TTP was significantly decreased in mutated KRAS patients (3 vs 5.5 months, P=0.015). Our study confirms that KRAS mutation is highly predictive of a non-response to cetuximab plus chemotherapy in MCRC and highlights the need to use sensitive molecular methods, such as SNaPshot or PCR-LCR assays, to ensure an efficient mutation detection.

Figure 1

Detection by SNaPShot and PCR-LCR assays of KRAS mutations not detected by direct sequencing. Direct sequencing of KRAS exon 2 from control DNA and tumour 12292. The black arrow indicates the nucleotide c.35 (A). SNaPShot detection of the c.35G>T (p.G12V) mutation in tumour 12292. Each peak corresponds to a specific extended primer. The red arrows indicates the peak specific of the c.35G>T mutation (B). PCR-LCR analysis of tumour 12292, using a dye-labelled primer specific for the mutant c.35G>C (p.G12A) or c.35G>T (p.G12V) KRAS allele. The arrow indicates the peak specific of the c.35G>T mutation (C). Note that the c.35G>T mutation detected by both the SNaPShot and PCR-LCR assays cannot be clearly detected by sequencing analysis alone.