Testing RAS Gene Mutations in Patients with Colorectal Cancer
Correct identification of the RAS oncogene variant is crucial for deciding the treatment of patients with colorectal cancer. Information on the prevalence of individual RAS gene mutations varies significantly in the literature, which may be due to different testing methods. The authors of the presented analysis focused on how the approach to testing RAS variants has evolved over time in Europe.
Why test mutations in the RAS gene?
Monoclonal antibodies against the epidermal growth factor receptor (EGFR) have significantly improved the survival of patients with metastatic colorectal cancer (mCRC). Observational studies have shown that patients with a mutation in exon 2 of the KRAS oncogene do not benefit sufficiently from anti-EGFR treatment. Further studies have shown that there are more mutations in the RAS gene affecting the efficacy of EGFR antibody treatment, and in 2013, the European Medicines Agency (EMA) therefore restricted the indication for EGFR antibodies only to patients with a wild-type RAS gene. The authors of the presented study aimed to determine how RAS gene testing evolved in Europe over the 5 years following the change in the indication for targeted treatment.
Analysis Methodology
A total of 239 laboratories from 44 countries participated in the external quality assessment of testing for metastatic colorectal cancer conducted by the European Society of Pathology (ESP) from 2013-2018. Testing was conducted once a year (not all laboratories participated each year). Each laboratory received 3 slides from 10 formalin-fixed paraffin blocks. These samples were evaluated by a pathologist in each laboratory, and DNA extraction and mutation analysis were performed. The number of misclassifications of mutations and test failures for individual laboratories were evaluated based on the testing methodology used.
Data for the analysis also came from a survey in which 33 participating laboratories provided detailed information on routine testing methods, annual numbers of analyzed samples, and counts of detected mutations in the RAS gene between 2013 and 2017.
Results
Testing failed in 1.6% of cases. The mutation status was correctly determined in 96.1% of RAS and BRAF gene tests. A total of 4.6% of RAS gene tests were false-negative. Between 2013 and 2018, there was a gradual decrease in the number of misclassified samples and technical failures.
The number of laboratories using next-generation sequencing increased from 6.9% to 44.6% over the 5-year period. Over time, more and more codons of the RAS gene were included in the testing, yet in 2018, 23.2% of laboratories did not offer complete RAS gene variant testing (exons 2, 3, 4).
Based on the survey with a total of 27,325 evaluated samples, the overall prevalence of RAS gene mutations in mCRC was 45.2% (95% confidence interval [CI] 44.6-45.8%).
Conclusion
Laboratories currently perform well, but it is expected that they will continue to strive for 100% success in determining mutation status. Standardized validation and verification procedures and internal quality controls should be used when introducing new methodologies.
In the largest published observational study to date, the prevalence of RAS gene mutations in patients with mCRC was approximately 45%, stable over time regardless of increasingly sensitive testing methods.
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Source: Dufraing K., Keppens C., Tack V. et al. Evolution of RAS testing over time: factors influencing mutation rates in metastatic colorectal cancer patients. Colorectal Cancer 2020; 9 (1): CRC14, doi: 10.2217/crc-2019-0013.
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