KRAS MUTATION ASSAY
Under the Ras gene family, the KRAS protein is produced by the KRAS gene. The KRAS protein functions as a GTPase in cell signal transduction. Mutation of the KRAS gene occurs by inheritance at birth or acquisition over a lifetime of a single nucleotide substitution. The KRAS gene encodes for proteins that modulate cellular activities through signal transduction. These activating mutations cause the gene product to remain active resulting in uncontrollable cell division, tumor growth and cancer. Multiple malignancies such as lung adenocarcinoma, colorectal carcinoma, and pancreatic ductal carcinoma are associated with the KRAS gene mutation. Although EGFR tyrosine kinase inhibitors (TKIs) can block EGFR activation, they cannot block the activity of the mutated KRAS protein. KRAS mutation testing is used to predict eligibility for colorectal and non-small–cell lung cancer (NSCLC) targeted therapies.
KRAS mutation detection and analysis is ordered for cancer patients to determine the best line of treatment. The National Comprehensive Cancer Network (NCCN) recommends KRAS mutation testing before starting EGFR-targeted therapy in both metastatic colorectal cancer and advanced non-small cell lung cancer1. Patients with KRAS mutations tend to be resistant to erlotinib and gefitinib. KRAS mutations are more likely found in adenocarcinomas, in patients who are smokers, and in Caucasian patients rather than East Asians. In NSCLC, tumors harboring KRAS mutations are predictive of poor prognosis and resistance to treatment with tyrosine kinase inhibitor therapy (TKI). KRAS and EGFR mutations are mutually exclusive. Over 99% of KRAS mutations in lung cancers are in codons 12 and 13. Early identification of these patients will allow appropriate and cost effective treatment decisions to be made by clinicians. Current estimates of the prevalence of KRAS mutation in lung adenocarcinomas range from about 15% to over 30%.
PRINCIPLE OF PROCEDURE
The KRAS assay detects 19 clinically relevant mutations in codons 12, 13, and 61. Primer extension products are analyzed using a multiplex microarray platform (Infiniti, AutoGenomics). The assay has a detection sensitivity of 1% mutant KRAS in a background of wild type genomic DNA. The accuracy of this method is what provides its usefulness in the management of cancer patients.
Testing is routinely performed on formalin-fixed, paraffin-embedded tissue subsequent to pathologist selection. Specimens can be submitted as unstained sections (4 microns thick) on unbaked slides or paraffin scrolls in a collection tube. FNA derived cell blocks are also acceptable. Frozen/fresh specimens are also acceptable. The specimen should be accompanied by an H&E stained slide.
TURNAROUND TIME: 5 DAYS
CPT CODE(S): 83907, 83891, 83900, 83901X8, 83914X38, 83912-26
- NCCN Clinical Practice Guidelines in Oncology™. Non-small cell lung cancer. v 2.2012.
- Available at:http://www.nccn.org/professionals/physician_gls/PDF. Accessed April 23, 2012.