• Detect mutations in the KRAS gene

• Determine eligibility for therapies targeting epidermal growth factor receptor (EGFR)

Mutations in the RAS gene family (HRAS, KRAS, and NRAS) have been observed in a variety of cancers (Table 1). They are activating mutations that result in continual signal transduction, stimulating downstream signaling pathways involved in cell growth, proliferation, invasion, and metastasis.

The KRAS gene encodes the KRAS protein that regulates 2 such signaling pathways: PI3K/PTEN/AKT and RAF/MEK/ERK. These pathways are targets of anti-cancer drugs that are currently in development. Drugs targeting EGFR, which controls these pathways upstream from KRAS, are already available. When bound to its ligand, EGFR stimulates tyrosine kinase activity, leading to activation of KRAS and the signaling pathways.

Current therapies targeting EGFR are used to treat colorectal cancer (CRC) and non-small-cell lung cancer (NSCLC) and employ either 1) monoclonal antibodies (eg, cetuximab and panitumumab) that prevent ligand binding and EGFR activation or 2) tyrosine kinase inhibitors (eg, erlotinib) that prevent activation of the signaling pathways. However, if the signaling pathways are activated independent of EGFR, as happens when the KRAS gene is mutated, these drugs are rendered ineffective.

KRAS mutations frequently found in neoplasms include those at exon 1 (codons 12 and 13) and exon 2 (codon 61). Mutations in KRAS codons 12 and 13 have been associated with lack of response to EGFR-targeted therapies in both CRC and NSCLC patients (Table 2).^2-4 The National Comprehensive Cancer Network (NCCN) recommends KRAS mutation testing before initiating EGFR-targeted therapies for CRC or NSCLC.^5,6 NCCN further recommends alternative therapies be considered for patients with KRAS mutations.^5,6

Quest Diagnostics can perform KRAS mutation testing on formalin-fixed, paraffin-embedded (FFPE) tumor tissue as well as bone marrow and whole blood (plasma). However, clinical studies that have assessed the impact of KRAS mutations on treatment response were based on testing tumor tissue only; therefore, the preferred sample type is FFPE tumor tissue.

• Patients with CRC or NSCLC who are being considered for treatment with an EGFR antagonist

• Polymerase chain reaction (PCR) and gene sequencing

–   PCR amplification of exon 1 (codons 12 and 13) and exon 2 (codon 61) of the KRAS gene

–   Gene sequencing of purified products

–   Computer analysis of sequencing data to determine mutation presence or absence

• Analytical sensitivity: 20% mutant allele in the background of wild-type allele

• Result reported: positive (homozygous or heterozygous for the mutation detected) or negative

In patients with advanced CRC or NSCLC, absence of a KRAS mutation predicts a greater likelihood of response to EGFR-targeted therapies and improved survival with such treatment. The presence of a KRAS mutation in codon 12 or 13 is associated with a high likelihood of resistance to therapies targeting EGFR (≥93%).⁷

This assay detects mutations at codons 12, 13, and 61 of the KRAS gene; polymorphisms or mutations at other locations that may be associated with drug efficacy or patient outcome will not be detected. Results should be interpreted in conjunction with other laboratory and clinical findings.