EGFR Mutation Testing (Lung Cancer)

Cobas® EGFR Mutation Test for In Vitro Diagnostic use (Roche).

The Cobas® EGFR Mutation Test is a real-time PCR test for the qualitative detection and identification of mutations in exons 18, 19, 20 and 21 of the EGFR gene using a DNA input of 150 ng. The test can detect 41 EGFR mutations including G719X (G719A, G719C and G719S) in exon 18; deletions and complex mutations in exon 19; S768I, T790M and insertions in exon 20; L858R in exon 21. The presence of mutations is detected with an analytical specificity of at least 98% and a detection limit of at least 5% mutant level in a background of wild-type genomic DNA.

The Cobas® EGFR Mutation Test is based on two major processes: (1) manual specimen preparation to obtain genomic DNA from one or two 5 µm thick sections of FFPE lung carcinoma tissue containing at least 10% tumor cells; (2) PCR amplification and detection of target DNA using complementary primer pairs and two oligonucleotide probes labeled with fluorescent dyes. Mutation detection is achieved through PCR analysis with the cobas z 480 analyzer (1, 2, 3).

Clinical Implication

Lung cancer is a leading cause of cancer death worldwide. Patients with non-small cell lung cancer (NSCLC) often present with advanced disease and treatment benefit with standard chemotherapy is modest. The introduction of therapies that target the epidermal growth factor receptor (EGFR) pathway in NSCLC, such as the tyrosin kinase inhibitor erlotinib (Tarceva), has begun to improve outcomes in patients with advanced NSCLC. Especially those NSCLC cases harboring activating mutations in the EGFR gene show response to anti-EGFR tyrosin kinase inhibitors. The highest response rates have been shown for exon 19 deletions, G719A/C, L858R and L861Q (4). Therefore, it is important to identify EGFR mutations in NSCLC.

Specimen Requirements

Acceptable specimens for the assay are formalin-fixed, paraffin-embedded NSCLC tissue specimens with a fixation time of 6-48 hours.

Volume

1 representative paraffin block is preferred. Alternatively, 8 unstained tissue sections are required. Of interest, if additional ALK FISH analysis is required (confirmation of ALK IHC positive case), two 3 µm thick unstained sections are required for ALK FISH analysis. 

Storage and Shipment Instructions

Maintain and ship specimens at ambient temperature.

Limitations

Insufficient tumor content may not allow the detection of EGFR mutations (< 10%); tumor content is evaluated prior to analysis and macrodissection is performed. Fixatives other than formalin or prolonged fixation time may give rise to inadequate results.

Special Requirements

None

Turn-Around Time

Five to 7 business days for slides and paraffin blocks respectively. In 2013, the mean turn-around-time was 4 business days (mainly paraffin blocks).

References

  1. Newton CR, et al. Analysis of any point mutation in DNA. The amplification refractory mutation system (ARMS). Nucleic Acids Res. 1989; 17(7): 2503-16.
  2. Lopez-Rios F et al. Comparison of molecular testing methods for the detection of EGFR mutations in formalin-fixed, paraffin-embedded tissue specimens of non-small cell lung cancer. J. Clin. Pathol. 2013; 66: 381-385.
  3. Pirker R et al. Consensus for EGFR mutation testing in non-small cell lung cancer: results from a European workshop. J Thorac Oncol. 2010 Oct;5(10):1706-13. 
  4. da Cunha Santos G et al. EGFR mutations and Lung Cancer. Annu Rev Pathol. 2011;6:49-69.