KRAS and NRAS are closely related RAS oncogene family members, and mutations in either gene at codons 12, 13 (exon 2), codon 61 (exon 3) and codon 146 (exon 4) result in increased levels of guanosine triphosphate-bound RAS proteins. Overactive RAS signaling promotes oncogenesis. In colorectal carcinoma (CRC), KRAS and NRAS mutations at these codons are found in up to 50% of cases and predict a lack of response to anti-EGFR therapy. Most RAS mutations are point mutations occurring in KRAS exon 2 (codons 12 or 13; about 40%). Other RAS mutation are less frequent with the most common mutations occurring in KRAS exons 3 and 4 and NRAS exons 2 and 3.
The BRAF V600E mutation is found in about 10% of metastatic colorectal carcinoma and has been associated with the presence of microsatellite instability. Overall, patients with BRAF mutant CRC have low response rates to conventional therapies and adverse prognosis. While BRAF V600-mutated melanomas are sensitive to BRAF-inhibitors, BRAF V600-mutated CRCs may not be as sensitive. Activation of EGFR in colorectal cancer could explain why colorectal cancers generally have a lower response to BRAF inhibitors. Therefore, it is advised to initiate combination therapy with EGFR- and BRAF-inhibitors.
Cobas® KRAS Mutation Test:
KRAS Mutation Test v2 (LSR):
The BRAF/NRAS Mutation Test (LSR) is based on two major processes:
Acceptable specimens for the assay are FFPE colorectal carcinoma tissue specimens with a fixation time of 6-48 hours.
One representative paraffin block is preferred. Alternatively, for resection specimens a minimum of 5 unstained tissue sections (5 µm thick) is required (full RAS testing).
Maintain and ship specimens at ambient temperature.
Insufficient tumor content may not allow the detection of KRAS/NRAS/BRAF mutations: 10% of tumor cells is required. Tumor content is evaluated prior to nalysis and macrodissection is performed.Fixatives other than formalin or prolonged fixation time may give rise to inadequate results.
5 to 7 business days for respectively slides and paraffin blocks.