Alternative Name
KRAS Exon 4 Sequencing
Test Description

Bi-directional sequencing of exon 4 of the KRAS gene corresponding to amino acids  R97 through Q150.  Codon 117 and 146 mutations are detected. For solid tumors, tumor enrichment is performed before extraction.  This test may be ordered separately or by reflex after standard KRAS Mutation Analysis. Testing is available separately or in combination with BRAF, HRAS and NRAS in the RAS/RAF Panel. Testing is approved for specimens from the state of New York.

Clinical Significance

This assay complements the standard KRAS Mutation Analysis of exons 2 and 3. Mutations in exon 4 are detected in approximately 1-4% of colorectal cancers. Exon 4 analysis is appropriate for detecting activating mutations that may confer resistance to EGFR-targeted inhibitors and predicts sensitivity to MEK inhibition.

Specimen Requirements
  • FFPE solid tumor tissue: Paraffin block is preferred. Alternatively, send 1 H&E slide plus 5-10 unstained slides cut at 5 or more microns. Please use positively-charged slides and 10% NBF fixative. Do not use zinc fixatives.
  • Fine needle aspirate (FNA): Requisition must note specimen is FNA. Fresh cells in suspension, unstained air-dried smears (approx. 6-8 slides), or FFPE cells blocks are acceptable if pathologist attaches note verifying sample has >30% tumor or abnormal cells (required). Minimum 10^6 cells.
Storage and Transportation

Use cold pack for transporting block during summer to prevent block from melting. Slides can be packed at room temperature.

CPT Code(s)*
Turnaround Time

7 days

Level of Service

*The CPT codes provided with our test descriptions are based on AMA guidelines and are for informational purposes only. Correct CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed.